The thyroid gland is a small, butterfly-shaped organ in the throat that is very important to health and wellbeing. The thyroid is part of the endocrine system, which is essentially a collection of glands. These glands produce hormones that regulate mood and other various functions in the body — and the thyroid gland is no different. 

"Thyroid hormones impact a host of vital body functions, including heart rate, skin maintenance, growth, temperature regulation, fertility and digestion,” said the late Dr. Jerome M. Hershman, former emeritus professor of medicine at the David Geffen School of Medicine at the University of California, Los Angeles.

But how big is the thyroid gland? What is its exact function? And what thyroid conditions should you know about? Keep reading to discover everything there is to know about this organ. 

Thyroid gland: Size

The thyroid gland is 2 inches (5 centimeters) wide and weighs between 20 and 60 grams (0.7 to 2.1 ounces), according to the U.S. National Library of Medicine. 

The gland stretches across the front of the neck, below the voice box. Like a butterfly, it has two wings called lobes that stretch around the windpipe. The wings are connected by a small piece called the isthmus.

Thyroid gland: Function

The thyroid gland controls just about every cell in the human body. It secretes hormones calcitonin, T4 (thyroxine or tetraiodothyronine) and T3 (triiodothyronine) into the bloodstream. The hormones control the rate at which cells and organs turn nutrients into energy and the amount of oxygen cells use. 

"In this way, the thyroid gland is the body's master metabolic control center," said Cindy Samet, a chemistry professor at Dickinson College in Carlisle, Pennsylvania. "Brain, heart and kidney function, as well as body temperature, growth and muscle strength — and much more — are at the mercy of thyroid function."

The thyroid also regulates the brain and nerve function and development, plus the function of the skin, hair, eyes, heart and intestines.

The thyroid works in conjunction with the pituitary gland. The pituitary gland regulates how many hormones the thyroid releases. 

The thyroid gland produces a large amount of T4, but that hormone is not very active. T4 is converted to T3 via an enzyme that removes one of its iodine atoms. 

"Although T3 is much more potent than T4, there is much evidence to support that people with hypothyroidism feel much better when they receive a combination treatment that includes a small amount of T3 with the commonly prescribed T4," Samet told Live Science.

Thyroid gland: Diseases and conditions

Thyroid conditions affect an estimated 20 million Americans and as many as 60% of people with a thyroid disease don't know they have a problem, according to the American Thyroid Association. 

"Women are particularly at risk for a thyroid issue," Hershman said. "One in eight women will develop a thyroid disorder during the course of their lives — that's five to eight times the rate in men."

Graves' disease

One of these conditions is called Graves’ disease, which was discovered by the Irish doctor Robert James Graves in 1835. Graves' disease is an autoimmune disorder. 

The immune system attacks the thyroid gland and makes it become overactive. An overactive thyroid is a condition called hyperthyroidism. A bulge on the neck, called a goiter, is a common symptom. The patient may also experience an increased heart rate, according to the National Library of Medicine (NLM).

Hypothyroidism 

Hypothyroidism, also known as underactive thyroid, is the opposite of Graves' disease. It occurs when the thyroid gland does not produce enough hormones. This can cause body functions to slow down or stop completely.  

Thyroid cancer

Cancer is another disease that can affect the thyroid. A 2017 study published in the Journal of the American Medical Association (JAMA) has found that between 1975 and 2013 the number of thyroid cancer cases diagnosed each year has more than tripled. Cases of advanced forms of the disease rose by about 3% each year while deaths rose by about 1% each year. 

A lump or swelling on your thyroid gland is called a nodule. Nodules can be harmless, but some can cause a production of too much hormone or be cancerous, according to the Endocrine Society.  

"Up to 70 percent of middle-age females and 40 to 50 percent of middle-age males have thyroid nodules, said Dr. Melanie Goldfarb, an endocrine surgeon and director of the Endocrine Tumor Program at Providence Saint John's Health Center in Santa Monica, California, and an assistant professor of surgery at the John Wayne Cancer Institute in Santa Monica. "You can also be born with an extra piece anywhere as high up as the base of your tongue,” Goldfarb adds. 

In some medical cases, such as cancer, the thyroid is removed. Humans can live without their thyroid if a hormone pill is taken daily.

Promoting good thyroid health

Science tells us that for the thyroid to remain healthy, it needs iodine to produce hormones, but just a little. 

"It turns out that one teaspoonful of iodine is enough for a lifetime of thyroid hormone production. But the thyroid gland needs a constant supply of iodine, so we must intake iodine in some form on a daily basis and not all at once," Samet said. Too much iodine can actually make the thyroid produce less hormones. 

The best way to get iodine is through eating healthy foods, such as seafood and dairy products. You can also get it by seasoning your food with iodized salt.

Additional resources

• Johns Hopkins: Thyroid Gland
• Digital Journal: Thyroid Gland Disorders Treatment Market- Asia Pacific Increases Thyroid Gland Disorders Treatment Demand, North America Continues to Lead It
• FDA: FDA Alerts Veterinarians and Pet Food Manufacturers about Potential Presence of Thyroid Hormones in Pet Foods and Treats
• NLM: Metastatic Tumors of the Thyroid Gland

Type 1 diabetes, once referred to as juvenile diabetes or insulin-dependent diabetes, is a chronic condition characterized by high blood sugar, or glucose.  

It occurs when the immune system mistakenly attacks the cells in the pancreas that make the hormone insulin, resulting in the inability of the body to produce enough insulin to keep blood sugars in check. Insulin is crucial for glucose metabolism; it helps shepherd sugar from the bloodstream into the body's cells for energy. Without insulin, glucose builds up in the blood, which, over time, can trigger life-threatening complications. (In people with type 2 diabetes, the body doesn't produce enough insulin, or does not use the insulin efficiently.) 

Type 1 diabetes is frequently diagnosed in children, adolescents or young adults, but it can develop at any age. People with this form of diabetes need to take insulin every day to stay alive. 

In 2019, 37.3 million Americans had diabetes (diagnosed and undiagnosed), of which 1.9 million had type 1 diabetes, according to the American Diabetes Association (ADA).

Causes & risk factors

The exact cause of type 1 diabetes is unclear, according to the National Library of Medicine (NLM). However, scientists think genetics and environmental factors, such as exposure to a virus, can cause the body to mistakenly attack key cells in the pancreas that make insulin.

Some known risk factors for this form of diabetes include a family history of type 1 diabetes, the presence of certain genes and geography; turns out,  the incidence of the disease is higher the farther away one is from the equator, possibly due to UV radiation and vitamin D deficiency, according to several scientific reports, such as a study published in 2017 in the journal Photochemical & Photobiological Sciences. And although the disease can develop at any age, it seems to often strike during two periods: in children between 4 and 7 years old, and in children between 10 and 14 years old, according to the Mayo Clinic.

• Related: Type 3 diabetes: Symptoms, causes and treatments

Symptoms & complications

The inability to produce insulin can result in a constellation of symptoms, which usually appear very quickly over a few days and weeks, according to the National Institute of Diabetes and Digestive and Kidney Diseases. These symptoms may include increased thirst, hunger and urination; blurred vision; fatigue; and unexplained weight loss.

"What we see in children is that they start being hungry and thirsty, and they're urinating a lot," Dr. Spyros Mezitis, an endocrinologist at Northwell Health in New York told Live Science. "They're feeling weak; they're losing weight."

Sometimes, the first sign of type 1 diabetes is a life-threatening condition called diabetic ketoacidosis (DKA), which occurs as a result of drastically low levels of insulin in the body, according to the NLM. Symptoms of DKA may include breath that smells fruity, dry or flushed skin, nausea or vomiting, stomach pain, breathing difficulties, confusion and inability to concentrate. DKA occurs when the body can't use sugar for energy, so it turns to fat instead. As a result of this process, compounds called ketones are released, causing the blood to become acidic and, in turn, toxic. If left untreated, DKA can be deadly.

Over time, uncontrolled blood sugar levels in people with diabetes can lead to a host of complications affecting major organs, triggering serious problems such as heart attack, stroke, blindness and kidney failure.

• Related: Which vegetables are good for diabetics?
• Related: Which fruits are good for diabetics? 

Diagnosis

If a doctor suspects diabetes, they will use a range of blood and other tests to make a diagnosis. For type 1 diabetes, in particular, the favored test is a random blood sugar test. The random blood sugar test measures blood sugar at the time of testing, and fasting is not required. A blood sugar level of 200 milligrams per deciliter (11.1 millimolar/liter) or higher indicates diabetes. But this measure and other blood tests don't discern whether the individual has type 1 or type 2 diabetes. 

Knowing the type of diabetes is crucial because it determines the treatment regimen, according to the Centers for Disease Control and Prevention (CDC). If type 1 diabetes is suspected, doctors may test for certain autoantibodies that attack the body' beta cells. Particular autoantibodies are common in type 1 diabetes, but not in type 2, and include: islet cell antibodies (ICA, against cytoplasmic proteins in the beta cell), antibodies to glutamic acid decarboxylase (GAD-65), insulin autoantibodies (IAA), and IA-2A, to protein tyrosine phosphatase, according to Johns Hopkins Medicine.) 

Other tests that help a doctor to diagnose diabetes, before determining the type, include:

• A fasting plasma glucose test reveals how effectively the body metabolizes glucose and requires the patient to fast for eight hours before taking the test. Normal blood sugar levels vary from person to person, but a normal range for fasting blood sugar is between 70 and 100 mg/dL (3.9 and 5.6 mmol/L), according to the World Health Organization. And a result of more than 126 mg/dL (7.0 mmol/L) of glucose in the blood signals diabetes.
• The oral glucose tolerance test requires the patient to consume an extra-sugary drink. Two hours later, the person undergoes a blood test. A result of 200 mg/dL or greater of glucose in the blood is considered a sign of diabetes.
• The A1C blood test shows average blood glucose over the preceding three months. The test measures glucose attached to hemoglobin, the oxygen-carrying protein in blood. The red blood cells that carry this protein live for about three months, so measuring them at a single time point provides a snapshot of the general level of glucose in the blood. An A1C result of less than 5.7% is normal; between 5.7% and 6.4% suggests prediabetes; and 6.5% or greater indicates diabetes.

Prevention & treatment

Scientists have not yet found a way to prevent type 1 diabetes, but researchers are currently working on ways to cease the destruction of insulin-producing cells in the pancreas in people who are newly diagnosed, the Mayo Clinic says. TrialNet — an international network of institutions and doctors working on type 1 diabetes research — has several clinical trials in the works for preventive measures. For instance, this network is testing whether a drug called Abatacept could delay or prevent the progression of the disease according to TrialNet. Another drug, called teplizumab, was found to delay the progression of type 1 diabetes for a median of two years, according to TrialNet.

Those who develop kidney failure and receive a kidney transplant, will sometimes also receive a transplant of pancreatic islet cells from an organ donor at the same time. Islet transplants may free them from the need to use insulin, potentially for many years, but requires taking lifelong immunosuppressive drugs according to the National Institute of Diabetes and Digestive and Kidney Disorders.

But the vast majority of people with type 1 diabetes require lifelong insulin therapy and will need to monitor their blood sugar levels frequently.

People with type 1 diabetes need to take insulin both to cover basic metabolic functions (called basal insulin) and to regulate the blood sugar produced by eating (called bolus insulin). To handle the blood sugar spikes caused by food, insulin shots are typically timed with meals and, once a routine is established, are done several times per day. Other options for administering insulin include a "pen," which allows for smaller doses (or boluses) of insulin to be injected, and a pump, which is attached to the body and delivers insulin throughout the day through a tiny tube that is inserted just beneath the skin surface, according to the ADA.

Insulin can cause low blood sugar, or hypoglycemia, which may cause feelings of weakness, hunger and headaches. Prolonged and severe low blood sugar can cause seizures, coma and death. 

There are several different types of insulin: Some last from about 18 hours to an entire day (called intermediate and long-acting, respectively); others, called rapid-acting insulin, enter the bloodstream in a few minutes and works most powerfully for an hour or twos; and regular- or short-acting insulin enters the bloodstream in about 30 minutes and is active for 3 to 6 hours, according to WebMD. People with type 1 diabetes may take long-acting insulin, which the body absorbs slowly, to provide the body’s basal metabolic need for insulin, while the rapid-acting insulin is used for meals.  

In 2016, the U.S. Food and Drug Administration approved the use of a so-called "artificial pancreas" — essentially a pump that uses a continuous glucose monitor to detect blood glucose levels and then automatically adjusts insulin dosing in response to those numbers, Live Science previously reported.

At the moment, there is no cure for type 1 diabetes, but research is ongoing. In order to rid someone of type 1 diabetes, the cure would need to both stop the immune system from destroying the body's beta cells and replace the already-lost beta cells successfully, according to the Juvenile Diabetes Research Foundation (JDRF). In 2021, the company Vertex announced a patient with type 1 diabetes was the recipient of a stem-cell therapy to replace their beta cells; and 90 days after the infusion, the person was using 91% less insulin, though the person also needs to continue immunosuppressive therapy to keep the body from killing off those replacement cells.

This article is for informational purposes only and is not meant to offer medical advice.

This article was updated on April 11, 2022, by Live Science contributor Natalie Grover, with additional reporting by Joseph Brownstein, MyHealthNewsDaily contributor.

Additional resources

• Learn more about the latest research on the hunt for a type 1 diabetes cure in this report by The New York Times.
• Read about how the prevalence of type 1 diabetes in American youth is on the rise in this report by the CDC.
• Check out the children's book "Year One with Type One: A True Story of a Boy with Type 1 Diabetes" (Owl Eye Books, 2018), by Mike Suarez, inspired by his son's journey with the disease.

Bibliography

"Statistics About Diabetes," American Diabetes Association
https://www.diabetes.org/resources/statistics/statistics-about-diabetes

"Type 1 diabetes," The Mayo Clinic
https://www.mayoclinic.org/diseases-conditions/type-1-diabetes/diagnosis-treatment/drc-20353017

"Type 1 Diabetes," National Institute of Diabetes and Digestive and Kidney Diseases
https://www.niddk.nih.gov/health-information/diabetes/overview/what-is-diabetes/type-1-diabetes

"Type 1 Diabetes," National Library of Medicine
https://medlineplus.gov/genetics/condition/type-1-diabetes/

"What Is Type 1 Diabetes?" Centers for Disease Control and Prevention
https://www.cdc.gov/diabetes/basics/what-is-type-1-diabetes.html

"Diabetic ketoacidosis," National Library of Medicine
https://medlineplus.gov/ency/article/000320.htm

"Diabetes Tests," Centers for Disease Control and Prevention
https://www.cdc.gov/diabetes/basics/getting-tested.html

The human body is a complex network of systems that work together to keep life-sustaining processes running smoothly. These systems break down food for fuel, clear away waste, repair damaged tissues and DNA, fight infectious germs and monitor the outside world so we can move through it safely. 

Many scientists spend their days working to understand how each bodily system performs its jobs, how the systems interact, and what can happen when one or more of them falter. Such malfunctions can stem from aging or disease, for instance, and through medical care, doctors aim to get derailed systems back on track. 

Here's a quick rundown of the systems of the human body, its vital organs and its "vestigial" organs, as well as a few fascinating facts about how the body works.

What are the different systems of the human body? 

Our bodies consist of a number of biological systems that carry out specific functions necessary for everyday living. Some organs and tissues play roles in multiple systems at once.

Related: Strange, two-faced brain cells confirmed to exist, and they may play a role in schizophrenia 

Circulatory: The job of the circulatory system is to move blood, nutrients, oxygen, carbon dioxide and hormones around the body. It consists of the heart, blood, blood vessels, arteries and veins. According to the Cleveland Clinic, the adult human body's network of blood vessels is more than 60,000 miles (around 100,000 kilometers) long. 

Digestive: The digestive system consists of a series of connected organs that together allow the body to break down and absorb nutrients from food and remove waste. It includes the mouth, esophagus, stomach, small intestine, large intestine, rectum and anus. The large intestine is home to microorganisms that are collectively called the gut microbiome and influence our health in various ways. The liver and pancreas also have roles in the digestive system because they produce digestive juices filled with enzymes to break down the components of food, such as carbohydrates, fats and proteins, according to the National Institute of Diabetes and Digestive and Kidney Diseases.

Endocrine: The endocrine system consists of a network of glands that secrete hormones — long-range chemical messengers that regulate how cells and tissue function — into the blood. These hormones, in turn, travel to different tissues and regulate many bodily functions, such as metabolism, growth and sexual function, according to Johns Hopkins Medicine. For example, the pancreas releases the hormones insulin and glucagon to regulate blood sugar. Conditions like diabetes and insulin resistance arise from the body having too little insulin or not responding to it adequately. 

Related: Meet the 'exclusome': A mini-organ just discovered in cells that defends the genome from attack

Immune: The immune system is the body's defense against bacteria, viruses and other pathogens that may be harmful. Components of the system include the lymph nodes, which contain infection-fighting cells called lymphocytes. These lymphocytes are one of many types of leukocyte, or white blood cell. The immune system also includes the spleen, the bone marrow and a gland called the thymus. The immune system can learn to recognize antigens — proteins on the surface of bacteria, fungi and viruses — and alert the body to their presence. Some immune cells make proteins called antibodies that attach to these antigens and mark invaders for destruction. 

Lymphatic: The lymphatic system includes the lymph nodes, lymph ducts and lymph vessels and is considered part of the immune system. Its main job is to make and move lymph, a clear fluid that contains white blood cells. The lymphatic system also removes excess lymph fluid from the body's tissues and returns it to the blood.

Nervous: The nervous system controls both voluntary actions, such as conscious movements, and involuntary actions,like breathing, and it sends signals to and detects signals from different parts of the body. Conscious actions are controlled by the somatic nervous system, while involuntary actions are controlled by the autonomic nervous system. The autonomic nervous system dictates whether we're in "rest and digest" or "fight or flight" mode. The nervous system can further be split up into the central nervous system (CNS), which includes the brain and spinal cord, and the peripheral nervous system, or the nerves connecting the CNS to every other part of the body.

Muscular: The body's muscular system consists of hundreds of muscles that aid movement, blood flow and other bodily functions, according to the Library of Congress. There are three types of muscle: skeletal, which is connected to bone and helps with voluntary movement; smooth, which is found inside organs and helps to move substances through them; and cardiac, which is found in the heart. The body's largest muscle by mass is the gluteus maximus, but the two latissimus dorsi are the largest in terms of surface area.

Related: Why is it harder for some people to build muscle than others?

Reproductive: The reproductive system allows humans to produce offspring. The male reproductive system includes the penis and the testes, which produce sperm. The female reproductive system includes the vagina, uterus and ovaries, which produce eggs. During fertilization, a sperm cell will fuse with an egg cell that, in a successful pregnancy, will then implant in the uterus. The fertilized egg will then mature into what's called a blastocyst, then an embryo and, finally, a fetus. A placenta forms to support this process. 

Skeletal: Our bodies are supported by the skeletal system, which contains between 206 and 213 bones in an adult human body, due to slight variations in people's anatomy, according to the medical resource StatPearls. These bones are connected by tissues called tendons, ligaments and cartilage. As infants, humans have about 300 bones, but some fuse together as the child grows. The skeleton not only helps us move but is  also involved in the production of blood cells and the storage of calcium. The teeth are also part of the skeletal system, but they aren't considered bones. The smallest bones in the body are found in the ear, and the largest is the femur, or thigh bone, which is also one of the heaviest body parts.

Respiratory: The respiratory system allows us to take in oxygen and expel carbon dioxide through breathing. It includes the lungs; trachea, or windpipe; and the diaphragm, a muscle that pulls air into and pushes air out of the lungs.

Urinary: The urinary system helps eliminate a waste product called urea, which is produced when certain foods are broken down. The system includes the two kidneys; two ureters, or tubes leaving the kidneys; the bladder; two sphincter muscles; and the urethra. The kidneys filter blood in the body to make urine that then travels down the ureters to the bladder and exits the body through the urethra.

Integumentary: The skin, hair and nails make up the integumentary system. Skin is the body's largest organ. It protects our innards from the outside world, serving as our first defense against bacteria, viruses and other pathogens, for instance. Our skin also helps regulate body temperature and eliminate waste through perspiration, or sweat. 

Related: Scientists discover new way humans feel touch 

What are the body's vital organs?

Click the purple circles to learn about the body's vital organs, including the brain, lungs, heart, liver and kidneys. They're considered vital because you need a functioning brain, heart, liver, at least one kidney and at least one lung to survive. That said, there are medical devices and treatments that can make up for a loss of function in these organs, at least temporarily — for example, ECMO machines can do the work of the heart and lungs, and dialysis can filter the blood of people with kidney failure.

Fast facts

• The average adult male body contains about 36 trillion cells, the average adult female body contains 28 trillion cells and a 10-year-old has about 17 trillion. 
• It's often said that there are 78 organs in the human body, but the number actually differs depending on whom you ask. 
• There's a popular idea that the body replaces itself every seven years. But that's not really true, because tissues renew themselves at different rates. 
• Oxygen is the most common element in the human body, followed by carbon. 
• The average adult body contains about 1.2 to 1.5 gallons (4.5 to 5.5 liters) of blood. 
• Humans' average body temperature has fallen slightly over time, so it's no longer 98.6 degrees Fahrenheit (37 degrees Celsius). 
• The most detailed map of the human brain to date contains more than 3,300 types of brain cells. 

What are vestigial organs?

There are arguably some parts of the human body that don't serve any useful purpose, such as the male nipple. That said, the usefulness of some organs is still up for debate, as scientists have often judged the worth of body parts before discovering their purposes. 

Broadly speaking, vestigial body parts are defined as those that have lost their original physiological significance to humans over the course of evolutionary history. The idea is that, while we inherited them from an ancient ancestor, we could really do without them in the modern day. 

Wisdom teeth are held up as one example of a vestigial body part, as the modern human jaw is often too small to accommodate a third set of molars. Some people also carry remnants of a vomeronasal organ that is largely thought to be nonfunctional in humans; animals use equivalent organs to detect each other's pheromones. 

Some scientists consider the human tailbone, or coccyx, vestigial because it's no longer a full-blown tail. But it's far from useless, as it still anchors many muscles, ligaments and tendons. And the appendix has gotten a bad rap for supposedly being both vestigial and useless, but more recently, scientists have uncovered possible functions for the long-maligned body part. 

Ever wonder why some people build muscle more easily than others or why freckles come out in the sun? Send us your questions about how the human body works to community@livescience.com with the subject line "Health Desk Q," and you may see your question answered on the website!

Editor's note: This page was last updated on April 5, 2024.

The endocrine system is the collection of glands that produce hormones, which are specialized proteins that regulate bodily functions. The endocrine system serves as the body's internal chemical signaling system, sending messages in the form of hormones to organs throughout the body via the circulatory system. Metabolism, growth and development, tissue function, sexual function, reproduction, sleep and mood are all examples of body functions that are regulated by hormones.

Endocrine system function

The endocrine system is made up of the hypothalamus, pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries and testes, according to Johns Hopkins Medicine. These glands produce and secrete hormones into the bloodstream for use elsewhere in the body. Although hormones circulate throughout the entire body, different types of hormones target different organs and tissues. 

Here's a summary of what each gland does: 

The endocrine system gets some help from other organs, such as the kidneys, liver and heart, which have secondary endocrine functions. For example, the main function of the kidneys is to filter the blood, but the kidneys also  produce hormones that assist in the production of red blood cells, and they metabolize, or process, several other hormones for use in other parts of the body , as described in a 2018 review published in the Methodist DeBakey Cardiovascular Journal. 

Endocrine system diseases

Endocrine system diseases or disorders occur as a result of hormone imbalance or when the body does not respond to hormones as it should. Stress, illness, infection or changes in blood composition can all influence hormone levels and in turn cause endocrine disorders, according to the National Institutes of Health (NIH). 

Here's a summary of some of the most common endocrine diseases: 

• Diabetes: The most common endocrine disease in the United States is diabetes, a condition in which either the pancreas does not produce enough insulin — the hormone that regulates blood sugar — or the body's cells don't respond to insulin properly.  Diabetes is typically treated with pills or insulin injections. 
• Reproductive hormone disorders: Reproductive hormone imbalances can affect fertility and may have long-term effects on metabolic, cardiovascular and bone health. For example, polycystic ovary syndrome in females is associated with hormone imbalances that cause a variety of symptoms, such as irregular periods, acne and fertility loss, according to the University of British Columbia. And in men, low testosterone results in low energy, reduced strength and libido, and increases the risk for low bone density.
• Hypothyroidism: Hypothyroidism occurs when the thyroid gland does not produce enough thyroid hormone to meet the body's needs. Insufficient thyroid hormone can cause many of the body's functions to slow or shut down completely. The disease is treated by surgically removing the damaged part of the gland. 
• Thyroid cancer: Thyroid cancer begins in the thyroid gland and starts when the cells in the thyroid begin to change, grow uncontrollably and eventually form a tumor. From 1990 to 2013, the global incidence of thyroid cancer increased by 20%, according to a 2020 review published in the journal Nature Reviews Endocrinology. The American Cancer Society predicts that there will be about 44,280 new cases of thyroid cancer in 2021 and around 2,200 deaths from thyroid cancer in the United States alone.
• Hypoglycemia: Hypoglycemia, also called low blood glucose or low blood sugar, occurs when blood glucose drops below normal levels. This typically happens as a result of treatment for diabetes when too much insulin is taken. The condition can also occur in people not undergoing treatment for diabetes, but such an occurrence is rare, according to the Mayo Clinic.

What is an endocrinologist?

Endocrinologists are medical doctors –– often gynecologists and pediatricians –– who specialize in typically one or two areas of endocrinology, such as diabetes or infertility. These specialists train to diagnose and treat specific endocrine disorders. Patients are usually referred to endocrinologists by their primary doctors.

To become an endocrinologist, a student needs to attend college as well as complete a degree in internal medicine before they specialize in endocrinology. In the U.S., this process takes about 13 years, before they are certified by the American Board of Internal Medicine.

Additional resources

• Learn about endocrine diseases from the National Institutes of Health
• The Merck Manual provides comprehensive information about the endocrine system
• Here's a Khan Academy video explaining how hormones flow through the body

This article was updated on Nov. 9, 2021 by Live Science Contributor Sarah Wild.

If you’d like more information on this topic, we recommend the following book:

That first drop of ice-cold water after a run in the scalding sun can be deliciously inviting. A glass of water after downing four others, however, probably isn't.

Those varied responses occur thanks to the brain, which makes sure we don't drink too much or too little water — two scenarios that would throw the body into dangerous territory.

But how does the brain know when to encourage you to stop or start drinking?

A new study conducted in mice suggests that a mysterious element in the gut may play a role by predicting how much you need to drink to satisfy the body. It then promptly notifies the brain, which, in turn, decides how thirsty to make you, a group of researchers reported today (March 26) in the journal Nature.

Thirst cells

In 2016, a group of researchers at the University of California, San Francisco (UCSF) found that when mice drink liquids, it prompts the mouth and throat to send signals to the brain, which shuts down the brain cells that dictate thirst. These "thirst cells" are found in a region called the hypothalamus, which regulates thirst, blood pressure and other bodily processes, and also in a small neighboring spot called the subfornical organ. [10 Things We Learned About the Brain in 2018]

The mouth and throat begin firing these signals within a few seconds of drinking something, although it typically takes from about 10 minutes to an hour for that water to actually enter the bloodstream and be circulated to thirsty cells throughout the body. So the brain needs to strike a balance — if it turns off the signals too fast, you won't get enough to drink.

"Somehow, the brain has a way to match these two different timescales so that you can very rapidly drink just the right amount of water to satisfy your body's needs," said study author Zachary Knight, an associate professor of physiology at UCSF and a Howard Hughes Medical Institute investigator.

How the brain does so was the question the researchers' study sought to answer.

The elusive talker

In the new study, Knight and his team implanted optical fibers and lenses near the hypothalamus of mouse brains, which allowed them to watch and measure when those thirst neurons turn on and off. [13 Tips for Staying Hydrated in the Summer Heat]

When they gave the mice salt water, the scientists found that the thirst neurons stopped firing almost immediately, as expected. But a minute or so later, those neurons switched back on.

The throat and mouth fire signals to the brain to begin quenching thirst no matter the type of liquid. But because salty liquids can dehydrate the body, the "on" signal likely came from somewhere else, after the throat and mouth turned the thirst neurons "off."

Following a hunch that these neurons might be getting the other signals from the gut, the researchers directly infused water — both salty and fresh — into the mice's stomachs, avoiding the mouth and throat signals all together.

They found that fresh water also made the neurons stop firing, but salt water didn't. What's more, when salt-water infused mice were given fresh water to drink, those thirst neurons first, as expected, switched off — but then quickly switched back on.

The results suggest that there are molecules in the gut that sense the salt content in liquids and use it to predict how much a drink will hydrate the body. This system, which only seemed to work when the mice were truly dehydrated, sends this information along to the brain within a single minute, and the thirst neurons twinkle on and off.

And sodium isn't the only compound that would set off the gut molecules, Knight told Live Science. "Anything that would change the osmolarity of the blood is detected by this system." (Osmolarity refers to how concentrated a liquid is.)

The control of thirst

The findings, if confirmed in humans, could benefit a range of people.

For example, Knight noted that our ability to regulate thirst decreases with age. "So [elderly people] fail to stay properly hydrated, and that can cause medical problems — especially, for example, during times of intense heat," he said.

The opposite can also hold true: " A large proportion of marathon runners tend to over-hydrate during a race," said Charles Bourque, a neuroscientist at McGill University in Canada, who was not a part of the study. "The reasons for this are not clear, but a weakening of this gut-to-brain signal might play a role."

In any case, the study "significantly advances what we know about the control of thirst," Dr. Bourque told Live Science. And because the results are consistent with data obtained from brain scans in humans, at least some of the findings are likely applicable to humans, he added.

Though mice and humans obviously differ in some brain structures, their hypothalami are very similar, Knight said.

The team also found that the thirst signals traveled along the main signal highway between the brain and the gut: the vagus nerve. When the researchers cut out this nerve in a later experiment, the thirst neurons didn't turn back on when the mice started drinking.

Though they don't know for sure, the team thinks that the signals are coming specifically from the small intestine, which is the spot that connects most strongly to the vagus nerve and is also in the "correct" timespot in the digestive process to activate those thirst nerves a minute or so after drinking water.

For their next project, the team hopes to figure out the origin of the signal.

• Top 10 Mysteries of the Mind
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Originally published on Live Science.

An out-of-this-world photo that was recently shared on Twitter resembles a galaxy of sparkling stars wrapped inside a colorful nebula.

But in reality, it's a fluorescent image of a male fruit fly's sex organs.

The image was captured by biologist Ben Walsh, a doctoral candidate in the Department of Evolution, Ecology and Behaviour at the University of Liverpool in the United Kingdom. He stained the testes of a dissected fruit fly with fluorescent dye to illuminate the organs' structures, which he then captured through a microscope using the camera on his iPhone, Walsh told Live Science in an email. [Magnificent Microphotography: 50 Tiny Wonders]

In the tweet, posted on Feb. 13, Walsh commented that the fruit fly testicles "kinda look like a galaxy." He later explained to Live Science that the yellow structures, which were "long and thin and coiled around themselves," were the testes' tissue wall.

"The blue clouds coming out of them at various points are sperm — in places, you can see bundles of sperm and even some individual heads," he said in the email.

When stretched out, each half of the testes measures over 0.08 inches (2 millimeters), "which is pretty much the whole length of the fly!" Walsh said. Fruit flies have the longest known sperm among all animals, but why they need such lengthy sperm is still a mystery, he added.

Walsh's research investigates how climate change affects fertility; he recently co-authored a study exploring the impacts of extreme temperatures on animal, plant and fungi reproduction, published Jan. 9 in the journal Trends in Ecology and Evolution.

His current work with fruit flies — which led to the image shared on Twitter — examines how temperature affects males' ability to produce viable sperm, a process known as spermatogenesis.

"By dissecting testes of the fruit fly Drosophila melanogaster and staining them with fluorescent dye, we can actually see bundles of sperm inside the testes, which allows us to count the number of sperm at different points of spermatogenesis," Walsh explained. This could reveal clues about what disrupts the flies' normal sperm production.

This isn't the first time the tiny organs and internal structures of a fruit fly have been revealed in illuminating images. Researchers recently developed a technique to capture images of fruit fly brains, creating stunning 3D images and animations that displayed the intricate interplay of neurons in a brain no bigger than a poppy seed, Live Science previously reported.

But even a single photo of fruit fly testes can generate wonder and astonishment, judging by the awed Twitter responses to Walsh's post. One bemused commenter took Walsh's joking galaxy analogy even further, writing, "What if our universe is contained in the left testicle of a fly in a greater dimension?"

To which Walsh tweeted in reply, "Then we're about to go places, because flies have a LOT of sex."

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Originally published on Live Science.

Corticosteroids are synthetic drugs that are used to treat a wide variety of disorders, including asthma, arthritis, skin conditions and autoimmune diseases. The drug mimics cortisol, a hormone that's naturally produced by the adrenal glands in healthy people.

Cortisol, commonly called the "stress hormone," is a steroid hormone (not to be confused with anabolic steroids, which are sometimes abused by athletes) that's released in response to stress. It's involved in a wide range of processes in the body, such as metabolism, inflammation, blood pressure regulation and bone formation, according to Johns Hopkins Medicine.

Corticosteroids work by decreasing inflammation and suppressing the immune system, according to Cleveland Clinic. Left untreated, excess inflammation can damage healthy tissue, as well as cause redness, swelling and pain.

The first use of corticosteroids dates back to 1948, when rheumatologists at the Mayo Clinic treated a patient who had debilitating rheumatoid arthritis, according to a 2010 article published in the journal Clinical Chemistry. The patient, who was treated with the then-experimental injectable drug, was able to walk out of the hospital after the third treatment and go on a 3-hour shopping spree, according to the author.

There are several types of corticosteroids, including cortisone, prednisone, dexamethasone, prednisolone, betamethasone and hydrocortisone. Cortisone was the first corticosteroid drug approved for use in the U.S., which happened in 1950, according to the U.S. National Institutes of Health.

Corticosteroid benefits

Corticosteroids are often used as a anti-inflammatory medications and immune suppressants to treat arthritis, asthma, autoimmune diseases (including lupus and multiple sclerosis), skin conditions (such as eczema and psoriasis), some types of cancer (such as leukemia), and the aftermath of organ transplant, according to the U.S. National Library of Medicine.

Depending on the specific treatment goal of the drug, it may be used orally, injected, inhaled or applied topically, according to the Mayo Clinic. Oral corticosteroids are typically used to treat and help control symptoms of chronic conditions, such as rheumatoid arthritis, by reducing inflammation throughout the body. Injected corticosteroids treat a specific location, such as inflammation or pain caused by tendinitis in a joint.

Corticosteroids are inhaled to treat asthma by reducing inflammation and swelling of the airways, and they can also help lower the risk or frequency of future attacks. Topical steroids are usually put into creams and ointments to treat and soothe skin conditions.

The immunosuppressive properties of corticosteroids are useful in treating diseases, such as lupus, in which the body's immune system can't properly distinguish between healthy cells and harmful ones. The drugs can also be beneficial in reducing the risk of rejection of a newly transplanted organ.

Corticosteroids are often used in conjunction with other treatments of lymphoid cancers, leukemia and tumors, where inflammation is a primary symptom, according to a 2016 article published in the journal Steroids. The corticosteroids prevent white blood cells from traveling to the site of inflammation, decreasing the swelling around tumors and the pressure on nerve endings to relieve pain, according to Chemocare. Corticosteroids are also prescribed to lessen the effects of chemotherapy symptoms such as nausea, vomiting and diminished appetite, although how the drugs work in those instances isn't fully understood.

Risks of corticosteroids

Although corticosteroids are effective medications, they can also have serious side effects.

For oral corticosteroids, these side effects may include glaucoma, fluid retention, high blood pressure and weight gain, according to the Mayo Clinic. There can even be psychological effects, including mood swings, confusion and behavior changes, the Mayo Clinic said. Taking the medication long term can also lead to cataracts, high blood sugar and diabetes, increased risk of infection from common bacteria and viruses, osteoporosis, suppressed adrenal-gland hormone production, and thin skin that has higher rates of bruising and slower wound healing.

When inhaled, corticosteroids may cause oral thrush (a fungal infection in the mouth) and hoarseness. These side effects are typically caused when some of the drug lingers in the mouth and throat after inhalation, instead of traveling to the lungs. The risk is typically minimized by rinsing and gargling with water, without swallowing, to clear any residual medication.

Application of topical steroids may lead to thin skin, red skin lesions and acne at the application site in some instances, according to the Mayo Clinic.

The side effects of injected corticosteroids may include temporary skin thinning, skin color loss and intense pain at the injection site, as well as facial flushing, insomnia and high blood sugar.

If a regiment of corticosteroids is prescribed by a doctor, there are ways to help minimize side effects. Patients should be sure to take the medication exactly as prescribed, eat a healthy diet with limited fat and salt and plenty of calcium and vitamin D, and exercise regularly to maintain strong bones and muscles, according to the University of Washington Orthopaedics and Sports Medicine.

Withdrawal symptoms may also occur if the medication is stopped suddenly or reduced too quickly. These can include muscle, bone and joint pain, nausea, weight loss and headache.

Long term use of corticosteroids may alter normal hormone production. For that reason, doctors may advise their patients to wear a medical bracelet or tag so that other medical professionals are aware of the patient's' corticosteroid use, and will alter treatment accordingly.

Additional resources:

• Learn more about the history of clinical research on corticosteroids from the National Institutes of Health.
• See the definition of corticosteroids and a list of inhaled corticosteroid medications from the American Academy of Allergy, Asthma and Immunology.
• Find out more about corticosteroids from the U.S. National Library of Medicine.

Since the early 2000s, researchers have noticed a troubling new trend in female development: Girls are entering puberty — developing breasts, pubic hair and getting their period — at younger ages.

So, what's driving the trend? Some researchers have long suspected that hormone-manipulating chemicals are the culprit. But these chemicals aren't necessarily coming from contaminated water or dangerous environments. Instead, they're found in products we use every day, including shampoo, makeup and nearly every kind of toiletry. [12 Hormone-Disrupting Chemicals & Their Health Effects]

Now, a new study, published Dec. 3 in the journal Human Reproduction, supports the possibility that the chemicals in these personal-care products are advancing the onset of puberty. In the study, public health researchers tracked a group of pregnant women and their children for 13 years, periodically measuring the concentrations of three groups of chemicals in the participants' urine. Their findings indicate that the odds governing whether a girl enters puberty earlier — which can have both physical and mental health effects — could be shifted even before children are born.

In other words, a pregnant woman's chemical exposure could play a role.

Indeed, the researchers suspected that chemical exposure in utero could influence the onset of puberty years after the infant’s birth, said study author Kim Harley, a public health researcher at the University of California, Berkeley.

But because so many women have detectable amounts of these chemicals in their bodies, the question wasn't whether or not someone was exposed to the chemicals, but rather how much they were exposed to them, Harley told Live Science.

In the study, the researchers looked at three kinds of so-called hormone disruptors — chemicals that interfere with the body's hormone system. The groups included phthalates, which are found in fragrances; parabens, which are preservatives used in cosmetics; and phenols, which, during the study period, was used in antimicrobial soaps.

Small shifts can add up

The study found that women with higher concentrations of one type of phthalate in their urine during pregnancy gave birth to girls who went on to develop pubic hair earlier than girls born to women with lower concentrations of the chemical in their urine. Similarly, women with high concentrations of phenol in their urine during pregnancy gave birth to girls who went on to begin menstruating sooner. When the researchers looked at the girls on their own, they found that nine-year-olds with higher paraben concentrations in their urine entered all three stages of puberty earlier those with lower concentrations. [7 Ways Pregnant Women Affect Babies]

Generally, the researchers found, the greater the exposure, the earlier the onset of puberty. For example, each doubling in maternal phthalate levels was associated with the early onset of the growth of pubic hair by about 1.3 months.

This shift may not seem like a big change. But there are multiple hormone-disrupting chemicals acting at once, and "it all adds up," said Karin Michels, a professor and chair of the department of epidemiology at the University of California, Los Angeles, who was not involved with the study. Michels has conducted similar research, which also found that these chemicals appear to hasten puberty.

And even a small change in puberty timing can increase the risk of certain cancers, Harley said; earlier periods are a risk factor for both breast cancer and ovarian cancer.

There's also the concern that too-young development could be challenging to cope with. "Developing early can put a lot of strain on girls that are physically looking mature but mentally still children — it changes the way they're treated in society," Harley said.

Still, Harley said, "We need more research to make sure what we found is real and not chance and holds out in other populations." For example, a majority of the women and girls in the study lived below the poverty line and the women worked in agriculture, where they could be exposed to a range of other chemicals. Harley said future studies plan to address pesticide exposure, but there isn't research showing that exposure to agriculture pesticides changes how hormone disruptors behave in the body, and most of the research on how pesticides impact development was done on chemicals that have now been almost completely phased out, such as DDT.

Michels, however, said that, based on her own research, lower-income individuals are generally exposed to more of these hormone-disrupting chemicals than others and are also more likely to be obese — which is known to shift puberty into an earlier start. Harley acknowledged this influence, too: Over half of the pregnant mothers and children in her study were overweight, Harley said, though her group accounted for that in their analysis.

As the research continues, consumers can mostly opt out of using these chemicals, Harley noted. The easiest to avoid is the phenol called triclosan, which now appears in only one brand of toothpaste. Shoppers can also look for products that are advertised as being "paraben-free", but phthalates will be harder to avoid, since they're often included in trade-secret scents, and companies don't always have to disclose phthalates as an ingredient, she said.

There also needs to be a boost in education efforts, Michels said. And not just on these chemicals, but the effects of all chemical exposures as well as the effects of childhood obesity: Mothers try to do their best by their children, Michels said, but sometimes, it's a matter of having the right information. As she pointed out, "Protecting children, from time of conception or even prior, is very important because they don't take charge of it themselves."

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Originally published on Live Science.

If you're already feeling stressed out, sorry, but there's one more thing you might need to worry about: A new study finds that stress may impair your memory now and quicken cognitive decline later in life.

And if that's not stressful enough, stress might also be tied to a slight shrinking of the brain, according to the study, published today (Oct. 24) in the journal Neurology.

In a study with more than 2,000 healthy, middle-age volunteers, doctors found that those with higher blood levels of the hormone cortisol — an indicator of stress — performed more poorly on memory tests and had a slightly shrunken brain volume compared to those with a normal level of the hormone. The effect was more evident among women in the study. [10 Things You Didn't Know About the Brain]

But before you panic, know that the researchers emphasized (stressed, really) that the findings do not mean that stress causes brain damage. Rather, the study reveals an association between stress and brain function that's consistent with laboratory-based studies on mice.

Don't stress — it's natural

The stress response is a natural part of life, as the bodymust react when confronted by danger or other threats. And cortisol is central to that stress response, said lead study author Dr. Justin Echouffo-Tcheugui, an assistant professor of medicine at the Johns Hopkins School of Medicine in Baltimore.

During stressful moments, cortisol levels rise and, together with another hormone called adrenaline, signal the body into making a fight-or-flight response. Specifically, cortisol increases glucose, or sugar, in the bloodstream; enhances your brain's use of that glucose for energy; and suppresses bodily functions that aren't immediately needed during an emergency, such as digestion, reproduction and growth. [11 Tips to Lower Stress]

Once the stressful event passes, cortisol levels should fall. This, however, isn't always the case, Echouffo-Tcheugui told Live Science. The body may still perceive stress or, for reasons not well understood, retain high levels of cortisol. Or, in this modern life, one's home or work life may cause daily stress.

Persistently higher cortisol levels can cause damage to the heart and skin. So, the idea that stress and higher cortisol levels could also affect memory and brain function is not surprising, Echouffo-Tcheugui said. Indeed, people with Cushing syndrome, a condition that's defined in part by a high and persistent level of cortisol, often experience poor memory, attention deficit, moodiness and depression.

Stress and the brain

In the new study, Echouffo-Tcheugui, who was based at Harvard Medical School while conducting the analysis, tapped into the Framingham Heart Study database, a massive, government-sponsored study that has followed the health of thousands of residents in the Framingham, Massachusetts, area for more than 70 years. Echouffo-Tcheugui and his colleagues identified 2,231 people with an average age of 49 who were free of dementia.

At the beginning of the study, each participant had a psychological exam and assessments for memory and thinking skills. Their memory and thinking skills were tested again an average of eight years later. At the end of the study,the participants also provided a blood sample, and about 2,000 of them had a a series of MRI brain scans to measure brain volume.

The researchers found that people with high levels of cortisol had lower scores on tests of memory and thinking skills than those with normal levels of cortisol. High cortisol was also linked to lower total brain volume.

Echouffo-Tcheugui said the study is only a snapshot of the effects of cortisol at one period in time for one group of people, largely of European descent. Yet, given the known deleterious effects of elevated cortisol levels on various body tissues, he said doctors and the public should pay heed to the potential for brain damage.

"Our research detected memory loss and brain shrinkage in middle-aged people before symptoms started to show" in ordinary, daily activities, said Echouffo-Tcheugui. "So, it's important for people to find ways to reduce stress."

Dr. Paul George, an assistant professor of neurology and neurological sciences at Stanford Medicine, who was not involved with the research, said the community-based study "raises many questions which need further exploration about how cortisol affects the brain and our cognition."

"One of the strengths is the assessment of these brain volumes using multiple imaging assessments to evaluate brain changes," George told Live Science. "The size of the study also adds to its impact, [and] they provided sound analysis to eliminate confounding factors such as depression."

The limitations, George added, are inherent in the nature of such epidemiological studies: The researchers cannot be certain of the cause, existence or persistence of stress, because they are relying on a one-time morning blood sample of cortisol levels.

Echouffo-Tcheugui said that he agrees with that assessment. Still, reducing stress can have a range of benefits, he said, whether it's accomplished through better sleep, exercise, relaxation techniques, or asking one's doctor about cortisol-reducing medication, if needed.

"There's nothing wrong in reducing stress," he said.

Follow Christopher Wanjek @wanjekfor daily tweets on health and science with a humorous edge. Wanjek is the author of "Food at Work" and "Bad Medicine." His column, Bad Medicine, appears regularly on Live Science.

Mona Lisa's smile is often described as enigmatic, but could the mysterious allure of this iconic painting actually be due to an underlying illness in "Lisa" herself?

At least one doctor thinks so. In a Letter to the Editor in the September issue of the journal Mayo Clinic Proceedings, a cardiologist and his colleague take a detailed look at the painting, and speculate that Lisa Gherardini, the subject of the painting, may have had hypothyroidism, or an underactive thyroid gland.

"The enigma of the 'Mona Lisa' can be resolved by a simple medical diagnosis of a hypothyroidism-related illness," Dr. Mandeep Mehra, medical director of the Heart & Vascular Center at Brigham and Women's Hospital in Boston, and his co-author, Hilary Campbell, an executive assistant at the University of California, Santa Barbara, proposed in the letter. "In many ways, it is the allure of the imperfections of disease that give this masterpiece its mysterious reality and charm." [25 Secrets of Mona Lisa Revealed]

Famed Renaissance artist Leonardo da Vinci painted "Mona Lisa" around 1503, according to the letter. It's thought that a wealthy Italian merchant, Francesco del Giocondo, commissioned da Vinci to do the painting of his wife, Lisa Gherardini, after the birth of the couple's child.

In 2004, some doctors hypothesized that Gherardini may have had a condition called familial hyperlipidemia, or high levels of fat (cholesterol) in the blood due to a genetic condition, which led to heart disease. They based this theory on several details in the painting, including skin lesions and swelling in Gherardini's right hand, which may be signs of the disease.

But in the new letter, Mehra and Campbell point out that Gherardini is thought to have lived to be 63 years old. If she indeed had familial hyperlipidemia, it's unlikely that she would have reached this advanced age, given the limited treatments available for the disease at the time.

Instead, the authors think that details in the painting point to hypothyroidism, a condition in which the thyroid gland doesn't make enough thyroid hormones to meet the body's needs. Thyroid hormones affect the body's metabolism, and an underactive thyroid gland can lead to a number of symptoms, including fatigue, weight gain, dry skin, muscle weakness, pain or swelling in the joints, thinning hair and, yes, high hyperlipidemia, according to the Mayo Clinic. The condition can also lead to a yellowing of the skin, as well as goiters, or enlargements of the thyroid gland.

The authors said that hypothyroidism could be a "unifying diagnosis" that would explain many features in the painting, including the subject's apparent yellowing skin; thinning hair and lack of eyebrows along with a receding hairline; a possible enlargement in the neck suggestive of a goiter; as well as the previously suggested symptoms of hyperlipidemia.

Mehra and Campbell also noted that Gherardini had given birth a few months before sitting for the portrait, and pregnancy can sometimes be a cause of hypothyroidism.

If Gherardini was indeed experiencing the effects of hypothyroidism, her famous expression may represent some of the conditions' symptoms, such as muscle weakness and reduced movement "leading to a less than fully blossomed smile," the authors wrote.

Still, it's important to note that there's no way to know for sure if Gherardini had hypothyroidism. There may be other explanations for the features in the painting. For example, her hair loss may have been due to intentional hair removal; and her yellowish skin may actually be the result of age-related changes to the painting itself, the authors wrote. And the famous "Mona Lisa" smile could be due to "da Vinci's experiments with a technique called sfumato, which allows tones and colors to fade into each other without discrete lines," Mehra and Campbell said.

"Certainly, we should also admit that our unifying theory may be as plausible as the multiple explanations provided, each open to individual and collective bias," they concluded.

Original article on Live Science.

A woman in Alabama who couldn't seem to lose weight turned out to have a massive tumor on her ovary, according to news reports.

The 30-year-old woman, Kayla Rahn, had experienced stomach pain and weight gain for months, and even had trouble with everyday activities like walking, according to local news outlet WSFA. "I couldn't even walk to my car without losing my breath," Rahn told WSFA.

Doctors told Rahn she simply needed to lose weight, but despite her weight-loss efforts, she continued to put on pounds.

Rahn's pain got so bad, she ended up in the emergency room, where doctors finally identified the problem: a 50-lb. (23 kilograms) mass on one of her ovaries. [27 Oddest Medical Cases]

Rahn had a type of tumor known as a mucinous cystadenoma, according to WSFA. This type of tumor is benign and arises from the tissue that forms the outer layer of the ovary, called the epithelium, according to a 2010 report of a similar case in Saudi Arabia. Mucinous cystadenoma tumors account for about 15 percent of all ovarian tumors.

These tumors are filled with a thick, gelatinous fluid. They can become quite large, with some reported to weigh more than 300 lbs. (136 kg), according to the reference book "Clinical Gynecologic Oncology, Eighth Edition." Just last month, doctors removed a similar 132-lb. (60 kg) ovarian tumor from a woman in Connecticut, Live Science previously reported.

Most often, these tumors occur in women ages 20 to 40, but cases have also been reported in teens and postmenopausal women, according to a 2014 review article.

Rahn's physician, Dr. Gregory Jones, an obstetrician/gynecologist at Jackson Hospital in Montgomery, Alabama, said he has seen cases of mucinous cystadenoma before, but he was surprised by the size of Rahn's tumor. "This is one of the largest I have ever seen or certainly removed," Jones told WSFA.

Rahn underwent surgery to remove the tumor last month, and she is now recovering. She's now able to wear clothes that she couldn't fit into before. "This dress I have on, I actually have not been able to wear in a year," Rahn said.

Original article on Live Science.

Polycystic ovary syndrome (PCOS) is the most common hormonal disorder in females of childbearing age, and it can sometimes make it hard to get pregnant, according to the online medical resource StatPearls.

The condition affects up to 5 million U.S. women of reproductive age, according to the Centers for Disease Control and Prevention (CDC), and it is named for the multiple cysts lining the outer edges of the ovaries. These aren't truly ovarian cysts, however. Instead, they're small, undeveloped egg follicles that may prevent regular ovulation. .

PCOS is characterized by high levels of androgens, or male reproductive hormones, and can come with a range of symptoms, including irregular periods, excessive weight gain and hair growth, and acne.

What causes PCOS?

No one knows the root cause of PCOS, and there is probably more than one, Dr. Marie Menke, a reproductive endocrinologist at University of Michigan Health, told Live Science.

One possible cause is that the ovaries make excess levels of certain sex hormones, including testosterone and anti-Müllerian hormone, Live Science previously reported. This, in turn, may drive many of the other symptoms. Why some ovaries produce excess sex hormones, however, is unclear.

Obesity and insulin resistance — the body's inability to effectively use insulin, a hormone that regulates blood sugar — also may play a role in triggering the disease. Others have proposed that children exposed to high levels of androgens in the womb may go on to have the disease.

Genes play a role, too: PCOS tends to run in families, and a woman whose mother or sister has PCOS is more likely to develop it. Women with a family history of type 2 diabetes are also more likely to develop PCOS, according to the World Health Organization.

PCOS and pregnancy

PCOS symptoms can show up as early as puberty and even after menopause. Many women find out they have the condition in their 20s and 30s, if they have trouble becoming pregnant. PCOS makes it hard to become pregnant because androgens prevent immature follicles from developing into mature eggs that can be released and develop into an embryo, according to the U.S. Department of Health & Human Services (HHS).

People who are hoping to get pregnant have a number of treatment options, including fertility medications, like clomiphene (also known by the brand names Clomid and Serophene), which are taken orally; or gonadotropins, such as follicle-stimulating hormone (FSH) or luteinizing hormone (LH), which are injected, according to the HHS.

PCOS symptoms

According to the HHS PCOS may include these signs and symptoms:

• Infertility: Women with PCOS do not ovulate regularly or frequently, so they have fewer chances per year to become pregnant
• Infrequent, irregular or absent menstrual periods
• Hirsutism, which is increased hair growth on the face, chest, stomach, thumbs or toes, likely caused by excess androgens
• Ovaries that are enlarged or have many cysts
• Acne or oily skin, also likely caused by excess androgens
• Weight gain or obesity
• Male-pattern baldness or thinning hair, another symptom of excess testosterone
• Acanthosis nigricans — thick, dark patches of skin on the neck, arms, breasts or thighs
• Skin tags, which are excess flaps of skin in the armpits or neck area
• Pelvic pain

Diagnosis & tests

Diagnosing PCOS can be challenging because symptoms vary a lot, Menke said. To be diagnosed with PCOS, a patient must experience at least two of the three main symptoms described below, Menke said.

1. Irregular menstrual cycles: Irregular, infrequent or no periods are caused by a lack of ovulation. For example, a woman may have fewer than nine periods a year or have unpredictable periods.
2. Higher than normal levels of male hormones (androgens).
3. Polycystic ovaries. However, some patients with PCOS have normal-appearing ovaries, and other women with cysts (fluid-filled sacs) on their ovaries may not have PCOS.

Complications

PCOS has been linked with a number of other health conditions. Whether PCOS actually causes these conditions isn't yet clear. These conditions include:

• Type 2 diabetes: More than half of women with PCOS develop diabetes by the age of 40, according to the CDC.
• Cholesterol abnormalities, such as high LDL ("bad") cholesterol and low HDL ("good") cholesterol, which can increase the risk for heart disease
• High blood pressure, which can affect the heart, brain and kidneys
• Metabolic syndrome, a group of risk factors for heart disease, stroke and diabetes, is twice as common in people with PCOS than the general population, according to information from the American Academy of Family Physicians.
• Sleep apnea: This condition, which can cause pauses in breathing during sleep, is more common in women with PCOS
• Anxiety or depression
• Diabetes or high blood pressure during pregnancy

Treatment & medications

It is difficult to treat all of the symptoms of PCOS at once, Menke said. So, she typically asks her patients, "What is your primary concern with PCOS?" and then focuses treatment on managing those symptoms first.

For example, if someone's main concern is excess hair growth, Menke said she would typically prescribe birth control pills, which can help reduce levels of androgens.

The treatment options available for PCOS can help manage symptoms, but they don't immediately go away, Menke said. According to the the Mayo Clinic, these treatment options may include:

• Birth control pills, which can control menstrual cycles, reduce androgen production and help clear acne.
• Fertility medications, which can stimulate ovulation in PCOS patients who wish to become pregnant. These drugs include clomiphene (also known as the brand name Clomid or Serophene), which are taken orally; or gonadotropins such as follicle-stimulating hormone (FSH) or luteinizing hormone (LH), which are injected.
• Anti-obesity drugs .
• Anti-androgens such as spironolactone or flutamide .
• Diabetes medications such as metformin that make the body more sensitive to insulin.

Additional reporting by Cari Nierenberg, Live Science contributor.

Men's testes were once thought to be free of bacteria, but a small new study from Italy suggests that microorganisms may live naturally in this part of the male reproductive system.

What's more, the findings suggest that this so-called testicular microbiome may be different in men with a type of infertility called azoospermia, who have no measurable sperm in their semen, than it is in fertile men.

Still, the findings are very preliminary, and much more research is needed to confirm if the testicular microbiome actually affects sperm production, the researchers said. But if the findings hold up, studies on the testicular microbiome might one day lead to the development of new therapies for men with azoospermia, who currently have few treatment options, experts say. [Trying to Conceive: 12 Tips for Men]

"These findings are actually surprising, because almost all medical textbooks mention that [the] human testes … is a microbiologically sterile microenvironment," said study lead author Massimo Alfano, a senior scientist at the Urological Research Institute at the IRCCS Hospital San Raffaele in Milan. But with new technologies, "for the first time ever, we [have] been able to quantify the bacterial DNA" in the testes, Alfano told Live Science.

"If confirmed and expanded, these results could support future … therapies for male factor infertility" such as those based on restoring a proper "testicular niche," Alfano said.

The study was published May 30 in the journal Human Reproduction.

Testicular microbiome

About 1 percent of all men, and 10 to 15 percent of men with infertility, have azoospermia, according to the Cleveland Clinic. Couples in which the man has azoospermia cannot become pregnant naturally, because there is no sperm in the man's ejaculate, said Dr. Sarah Vij, a urologist at the Cleveland Clinic who was not involved with the study.

"Those are the men that we really want to be able to help the most," Vij said, referring to men with azoospermia. "Some of those men [with azoospermia] have no options to have a biological child."

The most severe form of azoospermia is "non-obstructive azoospermia," which means the condition results from poor sperm production, rather than a blockage that prevents sperm from getting into the semen. The only treatment option for non-obstructive azoospermia is a surgery that attempts to retrieve sperm from the testicular tissue, which is not always successful, Vij told Live Science.

For the new study, the researchers analyzed testicular tissue from 10 men with non-obstructive azoospermia, as well as testicular tissue from five men without azoospermia who produced normal amounts of sperm. Among the men with azoospermia, half had successful surgeries that retrieved sperm, while half had unsuccessful surgeries that didn't retrieve any sperm.

The researchers found that the men without azoospermia had small amounts of bacteria in their testes, and these bacteria belonged to four main groups, called Actinobacteria, Bacteroidetes, Firmicutes and Proteobacteria.

The men with azoospermia had more bacteria overall in their testes, but their testicular microbiome was less diverse: The researchers found only two groups of bacteria — Actinobacteria and Firmicutes — in these men. What's more, the men who didn't have sperm retrieved during surgery had even less diversity in their microbiome, which was dominated mainly by Actinobacteria.

Avoiding surgery?

"I definitely applaud what they've done," Vij said of the study. "I think it has potential significance."

Currently, doctors do not have a way to predict which men with azoospermia will have successful sperm retrieval from surgery, Vij said. But the new findings raise the question of whether the testicular microbiome might help predict successful sperm retrieval. "If the microbiome can enable us to predict who is going to have success, we could probably spare some men surgery," she said.

In addition, if the findings are confirmed, it's possible that the testicular microbiome "could help guide future therapies for men, to give them another option" besides surgery, Vij said.

Still, even if future studies confirm the results, there are many more steps needed before the findings could be meaningful for patients. For example, the current study used testicular biopsies to describe the microbiome, but these procedures are invasive. "We have to figure out a way to assess the microbiome noninvasively, to have meaning" for patients, Vij said.

Additional studies would also need to examine whether changing the microbiome could have an effect on sperm production, she said.

In 2016, early research also suggested that women's fallopian tubes and ovaries may have microbiomes.

Original article on Live Science.

Though the thymus is a little-known organ in the body, it does some very important things. It is part of the lymphatic system, along with the tonsils, adenoids and spleen, and it's also part of the endocrine system. 

Function

The thymus produces progenitor cells, which mature into T-cells (thymus-derived cells). The body uses T-cells help destroy infected or cancerous cells. T-cells created by the thymus also help other organs in the immune system grow properly. 

These cells are so vital, they are often donated to those in need. "It (the thymus) is the primary donor of cells for the lymphatic system, much as bone marrow is the cell donor for the cardiovascular system," according to a paper, "The Thymus: A Forgotten, But Very Important Organ," published by the U.S. National Library of Medicine (NLM).

Size & shape

The thymus is located just below the breast bone. It is relatively large in infants and grows until puberty. In adulthood, it starts to slowly shrink and become replaced by fat, according to the National Institute of Neurological Disorders and Stroke. It can weigh only 5 grams in elderly adults.

As it grows smaller, it seems the organ becomes less important. "Removal of the organ in the adult has little effect, but when the thymus is removed in the newborn, T-cells in the blood and lymphoid tissue are depleted, and failure of the immune system causes a gradual, fatal wasting disease," according to Encyclopedia Britannica.

The thymus gets its name from its silhouette. It is shaped much like a thyme leaf, a common cooking herb. It has two separate lobes divided by a central medulla and a peripheral cortex and is formed with lymphocytes and reticular cells. The reticular cells form a mesh that is filled with lymphocytes.

Diseases & conditions

The most common thymus diseases are myasthenia gravis (MG), pure red cell aplasia (PRCA) and hypogammaglobulinemia, according to the NLM. 

Myasthenia gravis occurs when the thymus is abnormally large and produces antibodies that block or destroy the muscles' receptor sites. This causes the muscles to become weak and easily tired. 

Medications may be prescribed that help the communication between nerves and muscles, such as pyridostigmine (Mestinon). Corticosteroids like prednisone or immunosuppressants, such as azathioprine (Imuran), mycophenolate mofetil (CellCept), cyclosporine (Sandimmune, Neoral), methotrexate (Trexall) or tacrolimus (Prograf), may be used to inhibit the immune system. Your doctor may also prescribe other medications that alter your immune system, according to the Mayo Clinic.

Pure red cell aplasia is thought to be caused commonly by the patient's own immune cells attacking blood-forming stem cells. This can happen when the thymus has a tumor, according to The Aplastic Anemia and MDS International Foundation. Blood transfusions to increase red blood cell levels, corticosteroids and immunosuppressive therapy can all be treatments for this condition.

Hypogammaglobulinemia is a disorder where the body doesn't produce enough antibodies. Infants with this condition typically grow out of it without medical intervention. 

Thymus cancer is a disease in the thymus, rather than one caused by the thymus, like the previous examples. Symptoms may include shortness of breath, cough (which may bring up bloody sputum), chest pain, trouble swallowing, loss of appetite and weight loss, headaches, swelling of head face or neck, a bluish color to the skin and dizziness, according to the American Cancer Society. Thymus cancer is treated with surgery, radiation therapy or chemotherapy. This cancer is typically malignant in about 35 percent of cases.

Additional resources

• National Institutes of Health: Treatment of hypogammaglobulinemia in adults- A scoring system to guide decisions on immunoglobulin replacement
• Canadian Cancer Society: Thymus Cancer
• U.S. National Library of Medicine: Sonographic study of the thymus in infants and children

The pancreas is an abdominal organ that is located behind the stomach and is surrounded by other organs, including the spleen, liver and small intestine. The pancreas is about 6 inches (15.24 centimeters) long, oblong and flat. 

The pancreas plays an important role in digestion and in regulating blood sugar. Three diseases associated with the pancreas are pancreatitis, pancreatic cancer and diabetes.

Function of the pancreas

The pancreas serves two primary functions, according to Jordan Knowlton, an advanced registered nurse practitioner at the University of Florida Health Shands Hospital. It makes "enzymes to digest proteins, fats, and carbs in the intestines" and produces the hormones insulin and glucagon, he said.

Dr. Richard Bowen of Colorado State University's Department of Biomedical Sciences wrote in Hypertexts for Pathophysiology: Endocrine System, "A well-known effect of insulin is to decrease the concentration of glucose in blood." This lowers blood sugar levels and allows the body's cells to use glucose for energy. 

Insulin also allows glucose to enter muscle and other tissue, works with the liver to store glucose and synthesize fatty acids, and "stimulates the uptake of amino acids," according to Bowen. Insulin is released after eating protein and especially after eating carbohydrates, which increase glucose levels in the blood. If the pancreas does not produce sufficient insulin, type 1 diabetes will develop.

Unlike insulin, glucagon raises blood sugar levels. According to the Johns Hopkins University Sol Goldman Pancreatic Cancer Research Center, the combination of insulin and glucagon maintains the proper level of sugar in the blood.

The pancreas' second, exocrine function is to produce and release digestive fluids. After food enters the stomach, digestive enzymes called pancreatic juice travel through several small ducts to the main pancreatic duct and then to the bile duct, according to the Medical University of South Carolina’s Digestive Disease Center. The bile duct takes the juice to the gallbladder, where it mixes with bile to aid in digestion.

Location of the pancreas

"The pancreas is located in the upper abdomen behind the stomach," Knowlton said. The right end of the pancreas is wide and called the head. From the head, the organ tapers to the left. The middle sections are called the neck and body, while the narrow end on the left side of the body is called the tail. 

The Hume-Lee Transplant Center at Virginia Commonwealth University described the pancreas as "j-shaped." The portion of the pancreas called the uncinate process bends backward from the head and underneath the body, according to the Pancreatic Cancer Action Network.

Pancreas pain

Intense pancreatic pain is usually associated with acute pancreatitis. It can be hard to identify pancreas pain and evaluate pancreas diseases because the organ sits deep in the abdomen, according to The National Pancreas Association. Other signs that the pain may be pancreatic include jaundice, itchy skin and unexplained weight loss. If you are experiencing pancreas pain, consult your doctor.

Pancreatitis

The National Institutes of Health defines pancreatitis as inflammation of the pancreas, happening when "digestive enzymes start digesting the pancreas itself." It can be acute or chronic, but both forms should be taken seriously and may lead to additional health problems.

Chronic pancreatitis

There are up to 23 cases of chronic pancreatitis per 100,000 people per year worldwide. In just the United States, it results in more than 122,000 outpatient visits and more than 56,000 hospitalizations per year, according to the Cleveland Clinic.

"Chronic pancreatitis is a persistent inflammation (greater than three weeks) of the pancreas that causes permanent damage," Knowlton said. The condition is often caused by "heavy, ongoing" alcohol consumption, but she added that there are other causes, including "those that cause acute pancreatitis attacks." Other causes may be cystic fibrosis, high levels of calcium or fat in the blood and autoimmune disorders.

Symptoms include upper abdominal pain, nausea, vomiting, weight loss, and oily stools. According to Peter Lee and Tyler Stevens, in an article for the Cleveland Clinic, "clinically apparent" oily stools (steatorrhea) do not appear until "90 percent of pancreatic function has been lost."

"Chronic pancreatitis requires dietary modifications, including a low-fat diet and cessation of alcohol [intake] and smoking," Knowlton said. Chronic pancreatitis does not heal and tends to worsen with time, and "treatment options are mostly for pain relief." She added that treatments "may include a pancreas stent or, for severe cases, surgery (either a lateral pancreaticojejunostomy, or a Whipple procedure)." Pancreatiocojejunostomies are designed to decrease pancreatic leakage while the Whipple procedure removes the head of the pancreas where, according to the Mayo Clinic, most tumors occur. 

There may be a link between chronic pancreatitis and pancreatic cancer. According to the University of California Los Angeles Center for Pancreatic Diseases, "Recent studies reveal a 2-5 times increase in the incidence of pancreatic cancer in patients with chronic pancreatitis from a variety of causes."

Acute pancreatitis

"Acute pancreatitis is inflammation of the pancreas (lasting less than three weeks), that is most often caused by gallstones," said Knowlton. It usually comes on suddenly and disappears within a few days of treatment. In addition to gallstones, Knowlton said that causes "may include medications, high triglycerides, high calcium in the blood and high alcohol consumption."

Pancreas pain is the chief symptom of acute pancreatitis, according to Medscape. The pain is usually severe and sudden. It increases in severity until it becomes a constant ache. This pancreas pain is felt in the upper abdomen. The Mayo Clinic noted that the pain can radiate through to the back, and Knowlton pointed out that it might be worse after eating. Other symptoms of acute pancreatitis include nausea, vomiting, fever and diarrhea.

According to Knowlton, "This patient often looks acutely ill, and requires hospitalization (typically for three to five days), intravenous (IV) hydration, nothing by mouth (for bowel rest), pain medication, treatment of underlying conditions, and possibly a radiologic procedure called an endoscopic retrograde cholangiopancreatography (ERCP), which can more specifically target the problem." If the acute pancreatitis was caused by gallstones, doctors may recommend removing the gallbladder.

Pancreatic cancer

It is hard to diagnose pancreatic cancer early. The Mayo Clinic noted that symptoms typically don't occur until the cancer has advanced. Knowlton said, "Unfortunately, symptoms can be vague, but can include abdominal pain, jaundice, severe itching, weight-loss, nausea, vomiting, and digestive problems." 

Making matters even more complicated is the pancreas' deep-in-the-abdomen location. The NIH pointed out that as a result, tumors cannot usually be felt by touch. Because of the difficulty of early diagnosis and the rapidity with which pancreatic cancer spreads, the prognosis is often poor. 

Risk factors for pancreatic cancer include smoking, long-term diabetes and chronic pancreatitis, according to the National Cancer Institute.

According to the American Cancer Society, pancreatic cancer usually begins in the cells that produce pancreatic (digestive) juices or in the cells that line the ducts. In rare occasions, pancreatic cancer will begin in the cells that produce hormones.

According to the University of Texas MD Anderson Cancer Center, to diagnose pancreatic cancer, doctors typically conduct physical exams, blood tests, imaging tests, endoscopic ultrasounds and tests and biopsies. Treatment options include surgery, radiation, chemotherapy and therapies targeted to attack cancer cells without harming normal cells.

Artificial pancreas

When a person's pancreas isn't functioning properly or has to be removed, doctors may replace or supplement it with an artificial pancreas. These devices that automatically monitor blood glucose and provide the appropriate insulin doses are often called closed-loop systems, automated insulin delivery systems, or autonomous systems for glycemic control, according to the Food and Drug Administration. 

In a 2014 study published in the journal The Lancet Diabetes & Endocrinology, researchers found that an artificial pancreas offer people with type 1 diabetes a reliable way to keep glucose levels in check, when compared to other treatments. "Our study confirms that both artificial pancreas systems improve glucose control and reduce the risk of hypoglycemia compared to conventional pump therapy," study author Ahmad Haidar, of Institut de Recherches Cliniques de Montreal, said in a statement. [Artificial Pancreas May Improve Type 1 Diabetes Treatment]

Additional reporting by Alina Bradford, Live Science contributor.

Additional resources

• National Pancreas Foundation: About the Pancreas
• The Pancreas Center at Columbia University: The Pancreas and Its Functions
• Cleveland Clinic: Chronic Pancreatitis

Related pages about the human body

• Human Body: Anatomy, Facts & Functions

Parts of the human body

• Bladder: Facts, Function & Disease
• Human Brain: Facts, Anatomy & Mapping Project
• Colon (Large Intestine): Facts, Function & Diseases
• Ears: Facts, Function & Disease
• Esophagus: facts, Function & Diseases
• How the Human Eye Works
• Human Heart: Anatomy, Function & Facts
• Kidneys: Facts, Function & Diseases
• Liver: Function, Failure & Disease
• Lungs: Facts, Function & Diseases
• Nose: Facts, Function & Diseases
• Pancreas: Function, Location & Diseases
• Small Intestine: Function, Length & Problems
• Spleen: Function, Location & Problems
• Stomach: Facts, Function & Diseases
• The Tongue: Facts, Function & Diseases

Systems of the human body

• Circulatory System: Facts, Function & Diseases
• Digestive System: Facts, Function & Diseases
• Endocrine System: Facts, Functions and Diseases
• Immune System: Diseases, Disorders & Function
• Lymphatic System: Facts, Functions & Diseases
• Muscular System: Facts, Functions & Diseases
• Nervous System: Facts, Function & Diseases
• Reproductive System: Facts, Functions and Diseases
• Respiratory System: Facts, Function & Diseases
• Skeletal System: Facts, Function & Diseases
• Skin: Facts, Diseases & Conditions
• Urinary System: Facts, Functions & Diseases

Ovulation is the release of an egg from one of a woman's ovaries. After the egg is released, it travels down the fallopian tube, where fertilization by a sperm cell may occur. 

Ovulation typically lasts one day and occurs in the middle of a woman's menstrual cycle, about two weeks before she expects to get her period. But the timing of the process varies for each woman, and it may even vary from month to month. 

If a woman is hoping to become pregnant, she will want to keep track of when she may be ovulating. Knowing when a woman is ovulating each month is helpful because she is the most fertile — or able to become pregnant —around the time of ovulation. 

A couple will be more likely to conceive if they have sex a day or two before a woman ovulates and the day of ovulation, according to the March of Dimes.

Menstrual cycle and ovulation

At birth, a female fetus has 1 to 2 million immature eggs called oocytes inside her ovaries, which is all the eggs she will ever produce, according to the Cleveland Clinic. By the time a girl enters puberty, about 300,000 of these eggs remain. Approximately 300 to 400 of the remaining eggs will be ovulated during a woman's reproductive lifetime, the Cleveland Clinic says.

A likely sign that a woman is ovulating is that she is having regular, predictable periods that occur every 24 to 32 days, according to the Centers for Disease Control and Prevention (CDC). 

With every monthly menstrual cycle, a woman's body prepares for a potential pregnancy. The cycle is regulated by hormones, including the sex hormones estrogen and progesterone, as well as follicle-stimulating hormone and luteinizing hormone. Hormones play a key role in all stages of the menstrual cycle, allowing the ovum (egg) to mature and eventually be released. 

When a mature egg leaves a woman's ovary and travels into the fallopian tube, a sperm cell can fertilize the egg. Sperm can live inside a woman's reproductive tract for about 3 to 5 days after sexual intercourse, according to the Mayo Clinic. For pregnancy to take place, a sperm cell must fertilize the egg within 12 to 24 hours of ovulating, according to the Mayo Clinic. The fertilized egg then travels to the uterus, or womb, where it can attach to the lining of uterus and develop into a fetus.

During ovulation, the walls of the uterus also thicken to prepare for a fertilized egg. But if the egg is not fertilized, the uterine lining is shed about two weeks later, causing menstrual flow to begin. But simply having her period does not always indicate that a woman is ovulating.

"The most misunderstood thing about ovulation is the idea that if you are menstruating, it means that you are ovulating; and that is indeed not the case at all," said Dr. Mary Jane Minkin, a clinical professor of obstetrics, gynecology and reproductive sciences at the Yale School of Medicine.

Many women have an ovulatory cycle — the buildup of the lining of the uterus — because they are making estrogen. But when the buildup gets to a certain level, the lining just sloughs off, and a woman can bleed quite heavily, said Minkin. When a woman ovulates, she also makes the hormone progesterone, which results in a more controlled bleed.

Timing / ovulation clues

Many people mistakenly believe that ovulation always happens exactly 14 days after a woman's last period. But the timing of ovulation varies for each woman and depends on the length of her menstrual cycle. 

If a woman typically has 28-day menstrual cycles, she usually ovulated between days 13 to 15; If her cycle ranges between 27 and 34 days, ovulation usually occurs between days 13 to 20, according to The American Society for Reproductive Medicine. 

"Most women have no idea when they ovulate," said Dr. Christina Ramirez, an obstetrician and gynecologist in Garden City, New York.

Beside charting the timing on a calendar, a woman may have other clues that she could be ovulating. Her body may have one of the following three signs:

1. Change in vaginal secretions.

A few days before a woman ovulates, her cervix, which is the lower part of the uterus, produces a type of mucus that is thin, clear, slippery and stretchy. This change in cervical mucus occurs when ovulation is approaching and her ovaries are getting ready to release an egg. The day after ovulation occurs, cervical mucus undergoes another change and it becomes thicker and cloudy. 

2. Change in basal body temperature.

Keeping track of a woman's basal body temperature, which is taken in the morning before she gets out of bed, for two to three menstrual cycles may help predict when she is fertile. Shortly after ovulating, many women show a slight increase (about 1 degree F) in early morning body temperature. A woman is most fertile during the 2 to 3 days before her temperature rises, according to the Mayo Clinic. 

3. Rise in luteinizing hormone.

About 24 to 36 hours before a woman ovulates, her levels of luteinizing hormone increase. A rise in luteinizing hormone is a signal for the ovary to release an egg. This hormone increase can be detected by using an ovulation predictor kit, which can test a sample of urine in the days leading up to ovulation. When a rise in luteinizing hormones is detected, the test will show a positive result.

Fertile window

A woman is fertile — able to become pregnant — only during a certain part of her monthly cycle. The "fertile window" spans a 6-day period, the 5 days before ovulation and the day a woman ovulates, according to The American Society for Reproductive Medicine. Studies suggest that intercourse is most likely to result in a pregnancy when it occurs in the three days leading up to and including the day of ovulation.

Home ovulation test

If a woman is getting her period on a monthly basis, but not getting pregnant, it may be because she is not ovulating. An ovulation predictor kit can be helpful to see whether a woman is, in fact, ovulating. 

This kit, sold over-the-counter in drug stores, can test a woman's urine to detect if she is experiencing an increase in luteinizing hormone, which usually happens about 24 to 36 hours before ovulation occurs, according to the Mayo Clinic. 

A woman may want to begin using the kit about 10 days after the start of her last period, the March of Dimes recommends. 

"And if the test shows that ovulation isn't occurring, it's a great time to check in with your gynecologist: because getting women to ovulate is often quite straightforward," said Minkin. When ovulation is irregular or does not occur, doctors may try to induce the process by prescribing medication to stimulate a woman's ovaries to release an egg.

Ovulation problems

There are many reasons why a woman may have ovulation problems. Some women, for example, have blocked fallopian tubes due to pelvic inflammatory disease, endometriosis or surgery for an ectopic pregnancy, according to theU.S. Department of Health and Human Services.

An abnormal level of hormones can cause ovulation to be irregular or not occur at all, according to The American College of Obstetricians and Gynecologists. For example, polycystic ovary syndrome (PCOS), is a condition in which levels of certain hormones are abnormal and a woman does not get her period or it is irregular. Thyroid problems can also make the ovaries less likely to release an egg.

A woman who is underweight with a body mass index (BMI) of 18.5 or less may have irregular menstrual cycles and it could also cause ovulation to stop, according to the American Society for Reproductive Medicine. At the opposite end of the weight spectrum, obesity may also lead to irregular periods and irregular ovulation. 

In addition, the timing of ovulation can be affected by factors, such as stress and excessive exercise. Emotional or physical stress may delay ovulation or prevent a woman from ovulating. Getting too much intense physical activity can also inhibit ovulation, according to the Mayo Clinic. 

Problems with ovulation are just one possible cause for infertility, which affects about 12 percent of women in the United States between the ages of 15 and 44, according to the CDC. 

Additional reporting by Alina Bradford, Live Science contributor.

Additional resources

• U.S. National Library of Medicine: Hormonal Regulation of the Menstrual Cycle
• U.S. National Library of Medicine: Endocrine Regulation of Menstruation

If you're feeling stressed, a whiff of your romantic partner's shirt may help you feel more relaxed, a new study shows.

Researchers from the University of British Columbia (UBC) found that smelling a romantic partner’s clothing was associated with lower levels of the stress hormone cortisol in women's blood, according to the study, published Jan. 3  in the Journal of Personality and Social Psychology.

"Many people wear their partner's shirt or sleep on their partner's side of the bed when their partner is away, but may not realize why they engage in these behaviors," lead study author Marlise Hofer, a graduate student in the UBC Department of Psychology, said in a statement. "Our findings suggest that a partner's scent alone, even without their physical presence, can be a powerful tool to help reduce stress." [11 Tips to Lower Stress]

The researchers included 96 opposite-sex couples in the study. The men were asked to wear T-shirts for 24 hours, without wearing any deodorant or scented body products. They were also asked to not smoke and to eat only foods that wouldn't affect their body scent. After the T-shirts had been worn for a day, they were frozen to preserve their smells.

Then, the women were given two T-shirts to smell: an unworn T-shirt and one that belonged to either a stranger or the woman's own partner. (In other words, women were either given an unworn T-shirt and their partner's shirt to smell, or an unworn T-shirt and a stranger's shirt to smell.) In both groups, the women were not told whether either shirt was worn, or who wore the shirt.

Women tend to have a better sense of smell than men, which is why they were chosen to be the "smellers" in the study, the researchers said.

After smelling the two shirts, the women participated in a mock job interview and a mental math task; this was done to raise their stress levels. To measure stress, the researchers asked the women questions about how much stress they felt and collected saliva samples to measure cortisol levels, according to the statement.

In the experiment, the women who received a T-shirt worn by their partners, rather than strangers, had lower cortisol levels, the researchers found.

Among the women who received their partner's shirt, plus an unworn shirt, smelling the partners' T-shirts was linked to a significant reduction cortisol levels, compared with smelling the unworn shirts. In addition, the women who smelled their partners' shirts said they felt less stress both before and after the interview and math test, the researchers said.

Furthermore, the effect was greater in women who recognized that the scents belonged to their partners, suggesting the benefits of a loved one's scent are strongest when women know what they are smelling, according to the study.

However, smelling a stranger's T-shirt had the opposite effect: It resulted in higher levels of cortisol throughout the stress test compared with smelling the unworn T-shirt, the researchers said in the statement.

"From a young age, humans fear strangers, especially strange males, so it is possible that a strange male scent triggers the 'fight or flight' response that leads to elevated cortisol," Hofer said in the statement. "This could happen without us being fully aware of it."

The findings could be used to help people cope with stressful situations when they're separated from loved ones, the researchers said.

"With globalization, people are increasingly traveling for work and moving to new cities," senior study author Frances Chen, an assistant professor in the UBC Department of Psychology, said in the statement. "Our research suggests that something as simple as taking an article of clothing that was worn by your loved one could help lower stress levels when you're far from home."

Originally published on Live Science.

The thyroid is a butterfly-shaped gland that wraps around the throat and is part of the body's endocrine system. Between 1975 and 2013, the cases of thyroid cancer diagnosed yearly have more than tripled, according to a 2017 study published in the Journal of the American Medical Association (JAMA).

"While overdiagnosis may be an important component to this observed epidemic, it clearly does not explain the whole story," said Dr. Julie Sosa, one of the authors of the new study and the chief of endocrine surgery at Duke University in North Carolina.

The American Cancer Society estimates there will be 56,870 new cases of thyroid cancer (42,470 in women and 14,400 in men) in the United States in 2017, and around 2,010 deaths. Up to 60 percent of people with a thyroid disease don't realize there is problem, though, according to the American Thyroid Association. 

Types

According to the National Cancer Institute, there are four types of thyroid cancer: papillary, follicular, medullary and anaplastic. 

Papillary cancer is the most common form of thyroid cancer, followed by follicular cancer. However, follicular cancer is considered more malignant, or aggressive, than papillary, according to EndocrineWeb. Both types form in the follicular cells of the thyroid. Most of the thyroid tissue consists of follicular cells, which secrete the iodine-containing thyroid hormones thyroxine (T4) and triiodothyronine (T3), according to Johns Hopkins Medicine.

Medullary cancer forms in the C cells of the thyroid, which make the hormone calcitonin. While the other types of thyroid cancer tend to be slow-forming, anaplastic is a rare form of aggressive cancer in the thyroid.

Causes & symptoms

The causes of thyroid cancer vary. It can be passed on genetically, or it can be caused by radiation to the head or throat as a child, according to the National Cancer Institute. 

"Women are particularly at risk for a thyroid issue," said Dr. Jerome M. Hershman, a professor of medicine at the David Geffen School of Medicine at UCLA and author of the thyroid sections of the Merck Manual. "One in eight women will develop a thyroid disorder during the course of their lives — that's five to eight times the rate in men."

A malfunction in the thyroid, such as tumors from cancer, can cause a wide range of problems in the human body. 

"Thyroid hormones impact a host of vital body functions, including heart rate, skin maintenance, growth, temperature regulation, fertility and digestion," Hershman said.

Some symptoms that can be caused by thyroid cancer are neck pain, a hoarse voice and enlarged lymph nodes. Swelling in the area or lumps is not necessarily a sign of cancer, though. 

"Up to 70 percent of middle-age females and 40 to 50 percent of middle-age males have thyroid nodules, said Dr. Melanie Goldfarb, an endocrine surgeon and director of the Endocrine Tumor Program at Providence Saint John's Health Center in Santa Monica, California, and an assistant professor of surgery at the John Wayne Cancer Institute in Santa Monica. "You can also be born with an extra piece anywhere as high up as the base of your tongue."

Diagnosis

There are many ways a doctor may go about diagnosing thyroid cancer. Typically, a physical exam will be the first step. The medical professional will look for changes in the gland and ask about family history and exposure to radiation. Next, blood tests may be ordered to see if the thyroid is functioning properly. A biopsy, imaging tests and genetic disorder tests may be ordered to confirm a diagnosis, according to the Mayo Clinic.

Treatment

In many cases, treatment for thyroid cancer involves removing the entire gland surgically. Sometimes, medical professionals will opt to remove just a portion of the gland. The full or partial removal of the thyroid gland is called a thyroidectomy.

Lymph nodes may also be removed to check them for infection, according to the Mayo Clinic. Radioactive iodine, radiation therapy, injecting the cancer with alcohol, drug therapy or chemotherapy may also be ordered as treatment.

If the thyroid is removed, the patient will be given a prescription for a thyroid hormone medication called levothyroxine. This is usually a small pill that is taken daily for the rest of the person's life. Levothyroxine provides the hormones the thyroid would produce if it were still intact. It also suppresses the production of the thyroid-stimulating hormone (TSH) that comes from the pituitary gland. This is important because high TSH levels can stimulate remaining cancer cells to grow.

Additional resources

• Thyroid Cancer Survivors' Association Inc.
• National Library of Medicine: Thyroid Cancer
• Mayo Clinic: Thyroid Cancer-Preparing for Your Appointment
• American Thyroid Association: Thyroid Hormone Treatment

The adrenal glands affect metabolism, blood pressure, the immune system, sex hormones and the body's response to stress. The human body has two adrenal glands. About 1 inch by 2 inches (2.54 centimeters by 5.08 cm), they sit on top of the kidneys.

Along with the parathyroid glands, pituitary gland, thyroid gland, pancreas, ovaries (in females) and testicles (in males), the adrenal glands are part of the endocrine system. This system produces hormones that control just about every function in the body. 

Function

"The adrenal gland is an intricate part of the HPA (hypothalamus, pituitary, adrenal) Axis," Dr. Mark Engelman, permanent Clinical Consultant for Cyrex Laboratories, told Live Science. "This intimate physiological relationship is fundamental and critical to our wellbeing."

The hypothalamus acts as the body's thermostat, Engelman said. It senses most of the important physiological elements involved in homeostasis and sends out signals to correct perceived unhealthy variations. It connects directly to the pituitary gland, which essentially picks up the orders from the hypothalamus and sends out signals to various organs and glands, including the adrenals, to carry out these orders. The adrenal glands then produce a wide range of hormones, including estrogen, adrenalin and cortisol. 

"One of the primary activities of cortisol is to increase available glucose to the nervous system by breaking down protein and fat to glucose in the liver," Engelman said. "It helps block glucose uptake into tissues other than the central nervous system." 

Cortisol also has powerful anti-inflammatory and anti-allergy actions, according to Encyclopedia Britannica. It decreases the activities of the immune system to reduce inflammation conditions. Because of this, it is used to treat dermatitis, insect bites, inflammation from arthritis and ulcerative colitis.

One of the most important functions of the adrenal gland is the fight-or-flight response. When a person is stressed or frightened, the adrenal gland releases a flood of hormones, such as adrenaline and cortisol. These hormones increase the heart rate, elevate blood pressure, boost energy supplies, sharpen concentration and slow down other body processes so the body can run from or fight a threat.

Too much of a stress response is a bad thing, though. Too much exposure to elevated hormones from the adrenal gland can cause anxiety, depression, digestive problems, headaches, heart disease, sleep problems, weight gain and memory and concentration impairment, according to the Mayo Clinic.

Diseases & conditions 

There are many dysfunctions and diseases associated with the adrenal gland. One of them is the growth of tumors on the glands. These tumors can be benign or cancerous and can throw off the proper production of hormones. A tumor that causes the gland to create too much hormone is called a functioning tumor, while a tumor that causes too little hormone to be produced is called a nonfunctioning tumor. Approximately 4 to 12 out of 1 million people develop a type of adrenal tumor called adrenocortical carcinoma, according to American Society of Clinical Oncology. Some types of adrenal tumors may be linked to ADHD. 

A "trendy" disorder is adrenal fatigue. It currently is not an accepted diagnosis option for the medical community at large. The Mayo Clinic defines adrenal fatigue as "a term applied to a collection of nonspecific symptoms, such as body aches, fatigue, nervousness, sleep disturbances and digestive problems." These symptoms are thought to be caused by a wide range of adrenal problems, such as low hormone production.

Engelman said he thinks the signs and symptoms of adrenal fatigue are not related to the ability of the adrenals to work, but rather decreased stimulation from an over-taxed central nervous system. The entire physiological system is based on the concept of maintaining homeostasis. "I have heard from lecturers and read many theories and controversies about 'adrenal fatigue,'" Engelman said. "The ones that make the most scientific sense to me relate to the down regulation of central nervous system receptors to stress signals. This ultimately decreases downstream stimulatory signaling to the adrenal glands as a brain self-protective mechanism from the damaging effects of long term stress." 

Adrenal fatigue is thought to be a lesser form of adrenal insufficiency. Adrenal insufficiency (Addison's disease), a condition widely accepted by medical experts. It occurs when the adrenal gland does not produce enough hormones as a result of an underlying disease. Some symptoms are:

• Skin discoloration (hyperpigmentation)
• Unexplained weight loss
• Fatigue
• Lightheadedness
• Body aches
• Low blood pressure
• Loss of body hair

Additional resources

• National Institutes of Health: What are the Symptoms of Adrenal Gland Disorders?
• NIH: The Anti-inflammatory and Immunosuppressive Effects of Glucocorticoids
• The Journals of Gerontology: Associations with Negative Affect and Cortisol
• Phycology Today: Cortisol: Why “The Stress Hormone” Is Public Enemy No. 1

The pituitary gland is called the master gland of the endocrine system. This is because it controls many other hormone glands in the body. According to The Pituitary Foundation, without it, the body wouldn't reproduce, wouldn't grow properly and many other bodily functions just wouldn't function.

Size & location

The pituitary gland is located in the brain, between the hypothalamus and the pineal gland, just behind the bridge of the nose. It is about the size of a pea and is attached to the brain by a thin stem of blood vessels and nerve cell projections. The frontal lobe is the biggest part of the pituitary. It makes up 80 percent of the gland's overall weight, according to the Merck Manual. 

Function

The master gland controls the thyroid gland, adrenal gland, ovaries and testicles. While it may be in charge of these glands, it gets it orders from its neighbor, the hypothalamus. 

Basically, glands and hormones are a long communication chain in the body. The hypothalamus sends signals in the form of hormones to the pituitary gland, telling it just how much hormones are needed to send to the other glands. Then, the pituitary secretes hormones that signal to the glands how much hormones they need to secrete. 

The pituitary gland also produces hormones for organs in the body, as well. It creates: 

• Oxytocin for the uterus and mammary glands to stimulate contractions that aid in birth and milk production
• Vasopressin, an antidiuretic hormone, for the kidneys
• Beta-melanocyte-stimulating hormone that darkens the skin
• Endorphins for the brain and immune system to help inhibit pain sensations and regulate the immune system
• Growth hormones for muscles and bones 
• Enkephalins that help inhibit pain sensations in the brain
• Prolactin, which stimulates milk production in the mammary glands 

Most hormones are released every one to three hours and run in conjunction with the body's circadian rhythm. This means that hormone production is at its peak during the day hours and level off as night falls.  Other hormones rely on certain factors, such as the menstrual cycle, to determine production levels.

Diseases & conditions 

Most conditions of the pituitary gland are caused by cancerous or benign tumors and cysts. These growths are fairly common.  "One-sixth of people have a tumor or cyst of the pituitary," said Dr. Melanie Goldfarb, an endocrine surgeon and director of the Endocrine Tumor Program at Providence Saint John's Health Center and assistant professor of surgery at the John Wayne Cancer Institute in Santa Monica, California. 

Most of these tumors are benign and don't spread, though, according to the Mayo Clinic. A tumor can cause the pituitary gland to not produce enough hormones, a condition called hypopituitarism, or to produce too much hormones, or both at the same time. When hormone production is thrown off, other glands can malfunction and produce too much or too little of their hormones. Organs that rely on pituitary hormones can also be affected. This can cause a wide range of disorders, such as gigantism, galactorrhea, erectile dysfunction and central diabetes insipidus.

Computed tomography (CT) or magnetic resonance imaging (MRI) may be used to track the growth of a tumor, and simple blood tests can be used to diagnose a pituitary gland problem. 

In some instances, a tumor and some of the gland around it may need to be removed surgically. Luckily, this usually isn't a major problem.  "You can remove up to 95 percent [of the pituitary gland] and still have complete function," said Goldfarb.

Other than surgery, a doctor may treat tumors with hormone regulation through medication. Sometimes, nothing needs to be done to the growth because it isn't harming the patient. In these cases, medical professionals often wait and monitor the situation before taking action.

Additional Resources

• National Library of Medicine: Pituitary Gland
• National Library of Medicine: About Pituitary Tumors
• University of Maryland Medical Center: Pituitary Gland

Ovaries are the female gonads — the primary female reproductive organs. These glands have three important functions: they secrete hormones, they protect the eggs a female is born with and they release eggs for possible fertilization. 

Size & Location

Human females are typically born with two ovaries stemming from the uterus. Before puberty, ovaries are just long bundles of tissue. As the female matures, so do her ovaries. When mature, ovaries are about the size of a large grape, according to EndocrineWeb.

The ovaries lie on either side of the uterus against the pelvic wall in a region called the ovarian fossa. They are held in place by ligaments attached to the uterus.

• Related: Probiotics for vaginal health

Function

The ovaries have three functions. First, they shelter and protect the eggs a female is born with until they are ready for use. It is thought that women are born with their lifetime supply of eggs, but a study by the University of Edinburgh's School of Biological Sciences found that chemotherapy might spark the development of new eggs. 

"This study involves only a few patients, but its findings were consistent and its outcome may be significant and far-reaching," study researcher Evelyn Telfer, a professor at the University of Edinburgh's School of Biological Sciences, said in a statement. "We need to know more about how this drug combination acts on the ovaries, and the implications of this." [Can a Chemotherapy Drug 'Turn Back the Clock' in Women's Ovaries?]

Second, ovaries produce female reproductive hormones called estrogen and progesterone, and some lesser hormones called relaxin and inhibin. There are three different types of estrogen: estrone, estradiol and estriol. They are used by the body to help develop adult female characteristics, such as breasts and larger hips, and to aid in the reproduction cycle. Progesterone is also key to reproduction (more on that later). Relaxin loosens the pelvic ligaments so they can stretch during labor. Inhibin prevents the pituitary gland from producing hormones.

Third, ovaries release one egg, or sometimes more, each menstrual cycle. This process is called ovulation. Inside each ovary, there are follicles and inside of each follicle is a dormant egg. When a female is born, she has around 150,000 to 500,000 follicles in her ovaries. By the time she is sexually mature, the female will have around 34,000 follicles, according to the Encyclopedia Britannica. 

When a particular egg is stimulated to maturity by hormones released from the pituitary gland, the follicle migrates to the ovary wall. Here, the egg and the follicle grow and mature. When mature, they are ready for ovulation. Mature follicles, called Graafian follicles, can grow up to about 1.2 inches (30 millimeters) in diameter.

The follicle with the mature egg ruptures, releasing the egg into the nearest fallopian tube. From there, the egg travels to the uterus. The body produces the hormone progesterone to make the lining of the uterus thicker to be receptive to the incoming egg. This hormone is made by new cells growing where the old egg once was in the ovary. These cells are called the corpus luteum and act as temporary glands.

If there is no sperm, or if the egg just doesn't get fertilized, the body stops making progesterone around nine days after ovulation. Then the egg is flushed from the uterus during menstruation. Each menstrual cycle is around 28 days.

If the egg is fertilized, the corpus luteum — and then the placenta of the fetus — keeps producing progesterone. Not only does this hormone keep the uterus a hospitable environment for a growing egg, it also prevents the ovaries from releasing more eggs.

Occasionally, stress or other factors will prevent ovulation. When this happens, it is called a anovulatory cycle.

Diseases & conditions 

Most ovarian problems are caused by cysts. Ovarian cysts, growths on the ovaries, are common and most women will get them at least once, according to the Mayo Clinic. Most women don't even know when they have one because typically they are not painful or anything to worry about.  

Polycystic ovary syndrome (PCOS) is an ailment defined by multiple cysts growing on the outer edge of the ovaries due to a lack of hormones that allow an egg to be released from the follicle. This disorder can lead to infertility and other serious complications such as heart disease, diabetes or stroke.

Sometimes a cyst will become cancerous. One in 75 women will develop ovarian cancer, according to the American Cancer Society. There are current tests that can help detect a woman's likelihood of developing ovarian cancer. In some cases, women choose to remove their ovaries as a precautionary measure.

"If you have your ovaries removed due to certain hereditary cancer screening results such as BRCA, then we also remove your fallopian tubes because you can also get cancer from your fallopian tubes," said Dr. Sarah Yamaguchi, an OB/GYN at Good Samaritan Hospital in Los Angeles, California. "However, even with that done, you can still get primary peritoneal cancer which is very similar to ovarian cancer."

Additional resources

• Prevention: 5 Things You Need to Know About Having Your Ovaries Removed
• National Library of Medicine: Ovaries
• University of Utah: Removing Ovaries Might Increase the Risk of Colon Cancer

The testicles are the male gonads — the primary male reproductive organs. They have two, very important functions that are very important to the male reproductive system: they produce gametes, or sperm, and they secrete hormones, primarily testosterone. 

Anatomy of the testis

Testicles, or testes, are oval-shaped organs located in the scrotum, just behind the penis and right in front of the anus on male humans. Each testis weighs 0.35 to 0.5 ounces (10 to 15 grams), according to Virtual Medical Centre (VMC). They are typically 2 inches (5 centimeters) long, 1.2 inches (3 cm) wide and 1 inch (2.5 cm) thick. 

The scrotum is a loose sack of skin that protects the testicles and acts as a climate control system. The testes must be at a temperature slightly cooler than the body temperature for normal sperm development. Muscles in the wall of the scrotum allow it to tighten and relax, moving the testicles closer to the body for warmth or farther away to cool them, according to the Cleveland Clinic.

Each testicle consists of a series of small tubes, or tubules, that contain testosterone and sperm-producing cells. Seminiferous tubules house germ cells — the 23 chromosome cells that men replicate to produce sperm — and they are the site of sperm production, or spermatogenesis, according to VMC. These tubules are tightly coiled within the testis, and each testis may contain up to 900 tubules. The tubules are almost 20 inches (50 cm) long, and a typical testis contains up to half a mile (800 meters) of seminiferous tubules.

A fibrous tissue called the tunica covers the tubules. The tunica has three layers: the tunica vasculosa, the inner layer that consists of blood vessels and connective tissue; the tunica albuginea, which encases the testes and connects to the fibers that surround the epididymis, which transports sperm out of the testes and into the penis; and the tunica vaginalis, which contains fluid that reduces friction between the testes and the scrotum. 

Function

Besides sperm, testicles also produce male hormones called androgens. Androgens control how the male reproductive system grows, and the development of "masculine" body features such as beards and a deep voice. They also influence sexual functions. 

Testosterone is the most common form of androgen. It is responsible for the growth of male genitals and sperm production. Testicles in a healthy male can produce about 6 milligrams of testosterone each day, according to VMC. This isn't always the case, though.

"The testis make 200,000 sperm per minute on average," said Dr. Philip Werthman, a urologist and director of the Center for Male Reproductive Medicine and Vasectomy Reversal in Los Angeles, California. However, "as a man gets older and into his 30s, the amount of testosterone the testis produces starts to drop and continues to decline."

Diseases & conditions 

Typically, every male is born with two testicles. They form in the abdomen, and drop into the scrotum during their seventh month of gestation. 

Sometimes, though, the testicles do not drop, and the baby is born with a condition called undescended testicles. This happens for about 2 percent of males, and in 10 percent of those cases, both testicles are not in their proper position, according to the Mayo Clinic. Typically, this is a problem associated with preemies and the testicles often "drop" within a few months. If not, surgery may be required. 

Once testicles have dropped, they may not stay there. Retractile testicle is when a testicle moves into the groin area. Usually, a doctor can move the testicle back into its proper position, but if it is stuck, it is called an ascending testicle or an acquired undescended testicle. In this case, surgery may be needed to move it into proper position and stitch it into place.

A more serious condition of this organ is testicular cancer. It usually occurs in men 15 and 34 years old. In 2017, around 8,850 new cases of testicular cancer will be diagnosed and 410 deaths will be attributed to testicular cancer in the United States, according to the American Cancer Society. Though these numbers seem large, only around about 1 in 263 males get this type of cancer. Testicular cancer can be caused when the germline stem cells don't turn into sperm cells after a long period of time, according to National Geographic.

Promoting testicular health

Poor health can lead to lower sperm and testosterone production. Maintaining a healthy weight is a large part to good testicular health. According to the Centers for Disease Control and Prevention (CDC), the chance of infertility increases by 10 percent for every 20 pounds a man is overweight. Avoiding periodontal disease, STIs, stress, smoking, excessive drinking and a poor diet can also be good for a male's reproductive health. 

Keeping the testicles cool, just below normal body temperature, can also increase sperm count and quality, according to England’s National Health Service. An easy way to keep them cooler is by wearing loose clothing and by taking breaks often when in warm environments. 

Additional resources

• Mayo Clinic: Undescended Testicle Treatment
• Mayo Clinic: Retractile testicle
• National Cancer Institute: Testicular Cancer
• Cleveland Clinic: Disorders of the Testes

Heavy lifting at work may take a toll on women's fertility, a new study suggests.

In the study, which involved women undergoing fertility treatment, lifting or moving heavy things at work was linked with a reduction in biological markers of fertility. Similar links with decreased fertility were found in night-shift workers, the researchers added.

"Our study suggests that women who are planning pregnancy should be cognizant of the potential negative impacts that non-day shift and heavy lifting could have on their reproductive health," study co-author Lidia Mínguez-Alarcón, a research fellow in the Department of Environmental Health at the Harvard T.H. Chan School of Public Health in Boston, said in a statement.

However, the researchers noted that because their study included only women seeking fertility treatments, it's not clear whether the findings apply to women attempting to conceive without medical assistance. [Conception Misconceptions: 7 Fertility Myths Debunked]

Previous studies have found links between certain aspects of a person's job and fertility problems. For example, a 2015 study found a link between heavy lifting at work and irregular menstrual cycles, and a 2013 study found a link between night-shift work and an increased risk of miscarriage. Another study, published in 2015, found that female nurses who frequently lifted heavy loads at work took longer to become pregnant when they were trying to conceive, compared with women who never lifted heavy loads at work.

However, none of these earlier studies examined biological markers of fertility.

In the new study, the researchers analyzed information from nearly 500 women ages 18 to 45 (average age 35) seeking fertility treatment at Massachusetts General Hospital from 2004 to 2015. The participants were surveyed about their work schedules and the physical demands of their jobs. The researchers then assessed several biological markers of fertility, including the number of so-called antral follicles, which are small structures in the ovary that can be used to estimate the number of immature eggs remaining in a woman's ovaries. The researchers also looked at the number of mature eggs the ovaries produced in response to stimulation with medications (which was a part of the fertility treatment).

On average, the women in the study had about 12 antral follicles in their ovaries, and nine mature eggs after treatment with fertility medications.

But the women who reported lifting or moving heavy objects at work had 14 percent fewer mature eggs, and 5 percent fewer antral follicles, compared with the women who reported having never lifted or moved heavy objects at work.

In addition, the women who reported working night or evening shifts had 24 percent fewer mature eggs, compared with the women who reported working day shifts only.

"These findings have clinical implications, as women with fewer mature oocytes [eggs would have fewer eggs which are capable of developing into healthy embryos," the researchers wrote in the Feb. 7 issue of the journal Occupational and Environmental Medicine.

Exactly how heavy lifting could affect a woman's egg production and egg quality is not known, the researchers said.

Night-shift work may disrupt circadian rhythms, or the body's internal clock, which could explain the link between this type of work and lower egg yields, the researchers said.

The study took into account some factors that could affect women's fertility, including their age, body mass index and education level. But it's possible that there are other factors not addressed in the current study that could explain some of the results, the researchers noted. For example, the study wasn't able to take into account all of the aspects of the women's jobs that might impact their fertility (such as stress levels or exposures to certain chemicals).

More work is also needed to determine whether avoiding heavy lifting and night shifts could improve fertility, the researchers said.

Original article on Live Science.

A 50-year-old man who drank half a pint (about five shots) of vodka a day for more than a decade developed numerous calcium deposits in his pancreas that made him sick, according to a new report of the case.

The man went to the emergency room after he suddenly began vomiting blood, according to the report. He told doctors that he'd also experienced abdominal pain and diarrhea for the past two months, and reported his daily habit of vodka drinking, which he said he'd been doing for 15 years.

A CT scan of the man's abdomen showed that he had extensive calcium deposits in his pancreas, and he was diagnosed with chronic pancreatitis, a condition in which the pancreas is chronically inflamed.

Although these calcium deposits are often seen in patients with chronic pancreatitis, the degree of calcification seen in this patient is rare, said Dr. Yub Raj Sedhai, an internal medicine resident at Mercy Catholic Medical Center in Darby, Pennsylvania, who treated the patient. [27 Oddest Medical Cases]

Alcohol abuse over many years is the most common cause of chronic pancreatitis, according to the National Institutes of Health. Alcohol can damage cells in the pancreas, and also stimulate these cells to secrete enzymes that destroy the pancreatic tissue, which leads to inflammation, Sedhai said.

"Chronic alcohol use leads to a vicious cycle resulting [in] chronic inflammation of [the] pancreas," Sedhai told Live Science. Calcification of the pancreas happens because calcium gets deposited in the inflamed pancreatic tissue, he said. (Calcium is naturally present in the body, including in the blood stream. But even if your calcium blood levels are normal, the mineral can build up at sites where there is tissue damage, according to Harvard Medical School.)

Because the pancreas makes enzymes that help digest food, people with chronic pancreatitis may be unable to digest food properly, according to the NIH. But replacement pancreatic enzymes are available as prescription and over-the-counter medicines, which can help patients digest food and gain weight, the NIH says.

In this case, the man received pancreatic enzyme supplements and was enrolled in an alcohol abuse rehabilitation program, according to the report, which is published today (Feb. 1) in the New England Journal of Medicine.

People with chronic pancreatitis are advised to avoid drinking alcohol because drinking increases the risk for a relapse of symptoms, according to the NIH.

Original article on Live Science.

Your age may really just be a number: How well you're aging may be better revealed by a pattern of chemicals found in your blood than by that number. Indeed, a new study finds that certain "biomarker signatures" in the blood can signal people's risk of later developing some age-related health conditions.

A person's chronological age doesn't necessarily indicate their overall health or their risk for certain conditions. These biomarker signatures, by comparison, may offer better insight into a person's risk of age-related diseases and death over an 8-year period, the study found.

"These signatures depict differences in how people age, and they show promise in predicting healthy aging, changes in cognitive and physical function, survival and age-related diseases such as heart disease, stroke, type 2 diabetes and cancer," the researchers wrote in the study, published today (Jan. 6) in the journal Aging Cell. [7 Ways the Mind and Body Change with Age]

"We can now detect and measure thousands of biomarkers from a small amount of blood, with the idea of eventually being able to predict who is at risk of a wide range of diseases, long before any clinical signs become apparent," senior study author Dr. Thomas Perls, a professor of medicine at the Boston University School of Medicine, said in a statement.

In the study, the researchers measured the levels of 19 biomarkers in the blood samples of more than 4,700 people who were enrolled in an ongoing international research project called the Long Life Family Study. The people in the study ranged in age from 30 to 110.

The biomarkers included in the study were linked to many functions in the body, including those of the immune system, the endocrine system and the kidneys, and metabolism. Previous research had shown that the levels of these biomarkers vary with age, the researchers wrote.

Using a type of algorithm, the researchers determined that there were 26 different biomarker signatures among the study participants. Then, the researchers compared the participants' signatures with their rates of various diseases, and their overall health.

About half of the people in the study had "signature 1," the researchers found. This signature was deemed to be the reference point for all of the other signatures in the study, because the levels of the biomarkers lined up with what researchers would expect based on people's age and sex. For example, biomarkers associated with inflammation are thought to increase with age, while biomarkers associated with certain aspects of kidney function are thought to decrease with age.

Signature 2 was the "healthy aging" signature, and was found in about one quarter of the participants, according to the study. This signature was associated with better physical and cognitive functioning, a lower risk of type 2 diabetes and a lower risk of death over the 8-year study period compared with signature 1, the researchers found. [8 Tips for Healthy Aging]

Another eight signatures were associated with higher levels of risk for different diseases and outcomes compared with signature 1, according to the study.  The remaining 16 signatures were not associated with people's risk of disease as they aged.  

To confirm their findings about all 10 of these signatures, the researchers looked at available data on the levels of biomarkers from the participants in another study, the Framingham Heart Study. They found that seven of those 10 signatures successfully predicted the risk of the health conditions for the Framingham participants, the researchers found, adding further support to the findings.

The researchers hope that the biomarker signatures found in the study can be used in drug trials in the future, lead study author Paola Sebastiani, a professor of biostatistics at the Boston University School of Public Health, said in a statement.

Such trials could use the biomarker signatures "to detect the effects, or absence of effects [of a drug], that they are looking for" much earlier than current trials of drugs do, Sebastiani said.

The researchers noted that more studies on larger groups of people are still needed to further confirm the results. In addition, many more biomarkers could also play a role in the signature, and including them could perhaps lead to "even more powerful results," they wrote. 

Originally published on Live Science.

It's generally thought that women are born with a finite number of egg cells, and cannot grow new ones. But in a new study, researchers got a surprise when they found that women undergoing a particular chemotherapy had a much greater number of eggs in their ovaries than expected.

The reason for the finding isn't clear, but it suggests that the chemotherapy may spur the development of new eggs, the researchers say.

If confirmed, it would be the first time that scientists have seen new egg cells formed in adult women. And understanding exactly how this happens could aid in the development of fertility treatments that allow women to produce more eggs, the researchers said.

However, the researchers caution that the study was small, and the findings do not prove that the chemotherapy treatment caused the production of new eggs. In addition, it's not clear whether the greater number of eggs seen in these women after the chemotherapy treatment would help with their fertility. In fact, another part of the study found that the eggs from these women didn't grow as well in a lab dish, compared to eggs from healthy women. [Conception Misconceptions: 7 Fertility Myths Debunked]

"This study involves only a few patients, but its findings were consistent and its outcome may be significant and far-reaching," study researcher Evelyn Telfer, a professor at the University of Edinburgh's School of Biological Sciences, said in a statement. "We need to know more about how this drug combination acts on the ovaries, and the implications of this."

New eggs?

Women are born with all of the eggs they will use in their lifetimes, but the eggs need to mature inside structures called follicles. Typically, one follicle matures each month, and releases an egg. As women age, the number of follicles in their ovaries declines, which reduces their chances of pregnancy.

Some cancer treatments accelerate the loss of follicles, and thus hurt a women's fertility. But other cancer treatments don't seem to have an effect on fertility.

In the new study, the researchers originally set out to examine why a common chemotherapy treatment for Hodgkin’s lymphoma (a cancer of white blood cells) doesn't appear to affect fertility. The treatment is a combination of four chemotherapy drugs — adriamycin, bleomycin, vinblastine and dacarbazine — or ABVD for short.

The researchers analyzed samples of ovarian tissue donated by 8 women who had undergone ABVD, 3 women who had undergone a different type of chemotherapy and 12 healthy women around the same age.

Women who received the ABVD treatment had a much greater number of immature follicles in their ovaries —up to 10 times higher in some cases — than healthy women and those who'd received the other chemotherapy, the study found. Women who'd received ABVD also had a much greater number of follicles than would be expected based on their age.

The follicles in ABVD group also appeared younger — similar to those seen in girls before they go through puberty.

When the researchers tried to grow the follicle in a lab dish, those from the ABVD group didn't grow as well as those from the other two groups - only about 20 percent of follicles from the ABVD group showed growth, compared to 42 to 46 percent in the other two groups, the study found. This limited follicle development is also comparable to what's seen in prepubescent girls, the researchers said.

Future research

The researchers speculate that the ABVD treatment may active stem cells within the ovary to produce new eggs.

"It could be that the harshness of the treatment triggers some kind of shock effect or perturbation which stimulates the stem cells into producing new eggs," Telfer told the Telegraph.

But there could be other explanations, including that the egg follicles were damaged during treatment and split into two or more parts, David Albertini, laboratory director at the Center for Human Reproduction in New York, told the Guardian.

Future studies will examine the effect of each of the four chemotherapy drugs separately, to better understand the mechanism that may be leading to an increased number of follicles, the researchers said.

The study was published online Dec. 5 in the journal Human Reproduction.

Original article on Live Science.

Everyone raise a glass of chocolate milk!

Today's Google Doodle honors Frederick Banting, the doctor who first found a way to give insulin to patients with diabetes, nearly 100 years ago. Insulin is the hormone that tells cells to let in sugar from the blood, allowing the body to use energy from food as fuel. People with diabetes either do not produce enough insulin (Type 1 diabetes) or have body cells that don't respond well to insulin (Type 2 diabetes). 

Banting's work, which has saved the lives of millions of people with diabetes, garnered the Canadian doctor the Nobel Prize in Medicine in 1923. Today would have been Banting's 125th birthday. [Top 5 Nobel Prize Goof-Ups]

Insulin is made by the pancreas, which Banting began researching in 1920 as a captain in the Canadian army. At the time, researchers suspected that diabetes resulted from a deficiency in some hormone that came from certain clusters of cells in the pancreas, but they didn't know exactly how to extract that hormone. People were already calling the hormone insulin, according to the American Diabetes Association.

Banting believed he could extract this substance, and began his first experiments with dogs. The experiments involved closing off a duct in the dogs' pancreases, and then extracting insulin from those ducts.

"Intravenous injections of extract from dog's pancreas, removed from seven to 10 weeks after ligation of the ducts, invariably exercises a reducing influence upon the percentage sugar of the blood and the amount of sugar excreted in the urine ... the extent and duration of the reduction varies directly with the amount of extract injected," Banting and his colleague Dr. C. Herbert Best wrote in a 1922 paper published in the Journal of Laboratory and Clinical Medicine.

Eventually, Banting realized that waiting for the duct to produce the substance after closing it off wasn't necessary, and he was able to extract a small quantity of the hormone, according to a 2014 review article in the journal Diabetes Spectrum.

In 1921, he developed an alternate method of extracting insulin, by mixing ground cow pancreas and alcohol, then filtering rinsing, and sterilizing the resultant mixture. He tested the effects of this solution on dogs, according to the Diabetes Spectrum article.

The first patient to receive the medication was a 14-year-old boy named Leonard Thompson. When he came to see Banting, he weighed just 65 pounds and gave off the sickly sweet smell of acetone, a telltale sign that the body is in the later stages of the disease. The second person to receive the drug, in 1922, was a house officer named Ed Jeffery, whose blood sugar dropped after he received insulin.

Banting and his team quickly moved to make larger batches of the drug and entered into an agreement with drug maker Lilly. By 1923, the first commercial insulin was available, according to the article.

Invariably fatal

Before Banting's discovery, Type 1 diabetes, in which the body attacks the insulin-producing cells in the pancreas, was invariably fatal. Without it, sugar has no way to leave the blood and enter the body cells, so it accumulates in the blood, while the muscles and other tissues are starved for energy. The kidneys try to flush out the excess sugar in the blood by causing frequent urination, which leads to dehydration, causing people to be very thirsty, according to the American Diabetes Association.

Because the body can no longer use much of the sugar in the blood for energy, the body turns to burning fat, and people with the disease begin wasting away. Eventually, this process becomes a runaway reaction that leads to a diabetic coma and death.

The formal name of diabetes, diabetes mellitus, comes from the Greek word for a siphon, "diabainein," and from the word "mellitus," which means "like honey," because people who have the disease frequently urinate and their pee smells sweet. The disease has been known since antiquity, and many have tried to treat it. In ancient Egypt, doctors mixed water from bird ponds with various roots and herbs, such as elderberry, fibers from a local plant, beer, cucumber flowers and dates, according to Diabetes Spectrum. By 1916, Massachusetts scientist Elliott Joslin had showed that a high-fat, low carbohydrate diet could slow the progression of the disease, although people still succumbed to it eventually.

Original article on Live Science.

Women's fallopian tubes and ovaries were once thought to be free of bacteria, but a small new study finds that these microorganisms do live naturally in this part of the reproductive tract.

What's more, the findings suggest that women with ovarian cancer may have different, more harmful bacteria in their fallopian tubes and ovaries, but much more research is needed to confirm this idea, the researchers said.

In the study, the researchers analyzed tissue samples from 25 women who had been through menopause and were undergoing surgery to have their uterus, fallopian tubes or ovaries removed. Some of the patients had ovarian cancer, and some did not.

The samples were obtained under sterile conditions, and were immediately frozen in liquid nitrogen to ensure that they weren't contaminated with bacteria during collection, said study co-author Dr. Wendy Brewster, director of the University of North Carolina at Chapel Hill's Center for Women's Health Research. The researchers used genetic sequencing to identify the types of bacteria in the fallopian tubes and ovaries.

The results showed that there were bacteria in this part of the reproductive tract, and that there were different types of bacteria living in the fallopian tubes versus in the ovaries. [7 Facts Women (And Men) Should Know About the Vagina]

"We found that the upper reproductive tract is not sterile, and that bacteria do actually exist there," study co-author Temitope Keku, a professor of medicine at the University of North Carolina at Chapel Hill, said in a statement.

The study also suggested that there were differences in the bacteria in the women with ovarian cancer compared with the bacteria in the women without cancer. However, it's possible that these differences were due to chance, and more research is needed to confirm the finding and to investigate whether the bacteria in these sites could affect women's cancer risk, the researchers said. It's possible that the changes in bacteria happened after the patients developed cancer, the researchers noted.

The new study will be presented today (June 6) at the American Society of Clinical Oncology's (ASCO) annual meeting in Chicago. It has not yet been published in a scientific journal.

To confirm their findings, the researchers plan to repeat their study in a larger group of women, Brewster said.

The study adds to other recent evidence that the fallopian tubes and ovaries are not sterile. A study published in the May 2015 issue of the journal Obstetrics & Gynecology also found bacterial colonization in the upper parts of the female reproductive tract.

Original article on Live Science.

Twins tend to run in families, and now researchers have identified two genes that make women more likely to conceive nonidentical twins.

Both genes are related to the production and processing of the hormone that helps oocytes (egg cells) mature.

"There's an enormous interest in twins, and in why some women have twins while others don't," study co-author Dorret Boomsma, a biological psychologist at Vrije Universiteit Amsterdam, said in a statement. "The question is very simple, and our research shows for the first time that we can identify genetic variants that contribute to this likelihood." [Seeing Double: 8 Fascinating Facts About Twins]

Odds of twins

There are two ways that a woman may conceive twins. In one case, her ovaries release two eggs at the time of ovulation, and both are fertilized and become embryos; this results in fraternal, or nonidentical, twins. In contrast, identical twins are conceived when one embryo splits into two early in its development.

In very rare circumstances, more unusual twinning can occur: Doctors have identified semi-identical twins (who were formed from the same egg but two different sperm), and even identical triplets and quintuplets.

Scientists have long known that women who have a family history of fraternal twins — especially among their female relatives — are likelier to have twins themselves, suggesting that genetics plays a role. And twins are extremely common in some populations, such as the Yoruba people of West Africa, while it is much rarer in other populations, such as those from Asia. Older women and women who undergo fertility treatments are likelier to have twins as well.

However, teasing out the genetic underpinnings of twinning proved difficult.

Maturing eggs

To look for which version of genes might increase the likelihood of having twins, Boomsma and her colleagues analyzed the genomes of 1,980 women who had spontaneously conceived fraternal twins, and compared them to the genes of 12,953 women who bore singletons. 

They identified certain variants of genes that occurred much more commonly in the women who bore twins.

One variant, in a region of DNA near a gene called FSHB, seemed to be associated with producing higher levels of follicle-stimulating hormone — a chemical that helps an egg mature. (During each cycle, a woman typically releases an egg only after it has sufficiently matured.) With more FSH, the odds of two eggs being released per cycle — one from each ovary — may increase, the researchers hypothesized.

A second variant, in a gene called SMAD3, seemed to alter how receptive the ovaries are to FSH signaling. Women with this variant may produce average levels of FSH, but have ovaries that are more sensitive to the hormone, triggering the release of two oocytes per month.

"This genetic variant is totally novel and hadn't been shown before as a candidate gene for twinning," Cornelis Lambalk, a gynecologist at VU Medical Center Amsterdam, said.

Still, these two gene variations are only part of the puzzle. Together, they increase a woman's odds of having twins by only about 29 percent, suggesting that many other genes may be involved in the process, Boomsma said.

Follow Tia Ghose on Twitterand Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

A body part that many would wish away — their love handles — can be turned it into life-saving transplant: Researchers reprogramed fat cells from a person's waistline into pancreatic cells capable of producing the crucial hormone insulin.

If further testing shows that the cells are safe to implant into a person's body, and effectively produce insulin once they are there, they could one day be used to treat people with either type 1 or type 2 diabetes, experts say.

In a petri dish, researchers coaxed these reprogrammed pancreatic cells, called beta cells, to produce ample amounts of the hormone insulin, which helps the body turn food into fuel for muscles and organs such as the brain.

"We're very confident that we're the closest to natural beta cells which you can get," said study co-author Martin Fussenegger, a bioengineer at ETH Zurich, a science and technology university in Switzerland. [Inside Life Science: Once Upon a Stem Cell]

Blood sugar regulation

Normally, when food is broken down, levels of glucose (or sugar) rise in the blood, and in response, the cells of the pancreas produce insulin and release it into the bloodstream. Insulin then binds to receptors on cells throughout the body, essentially unlocking them and allowing body cells to absorb glucose from the bloodstream and use it for energy. 

But in people with type 1 diabetes, the immune system mistakes the insulin-producing beta cells in the pancreas for foreign invaders, and often early in life, it systematically destroys them all. People with type 1 diabetes need lifelong injections of insulin to survive.

In those with type 2 diabetes, the pancreas continues to produce insulin, but the insulin receptors on body cells grow misshapen and no longer bind insulin as well, meaning the cells develop insulin resistance and cannot take in sugar efficiently. Up to a point, the pancreas can compensate for this by cranking out more insulin to offset insulin resistance. But at some point, the pancreas simply can't keep up with the body's insulin needs, and people develop type 2 diabetes.

For decades, researchers tried to find ways to treat people with type 1 diabetes by implanting pancreatic cells from people who had died. However, there is a shortage of pancreatic cells for transplant, and people who received these transplants had to take powerful immune-system-suppressing drugs to prevent the body from rejecting the foreign tissue.

Stem cell reprogramming

To get around that obstacle, some researchers have focused on finding ways to reprogram a person's own cells to become pancreatic beta cells. For instance, earlier this year, researchers turned skin cells in insulin-producing beta cells.

The first step in this line of research is to take cells from a patient and turn back the clock on them, so they are stem cells, meaning they can turn into many different cell types. Researchers then have to persuade the cells to become pancreatic beta cells, through a process called differentiation. [How Stem Cell Cloning Works: Infographic]

In previous work, researchers "threw all kinds of chemicals and factors on them to make them differentiate, and that was kind of trial and error," Fussenegger told Live Science.

The cells that resulted acted similar to, but not exactly like, normal human pancreatic beta cells. For instance, the cells did not produce as much insulin as normal cells do in response to rising blood sugar levels, Fussenegger said.

More exact replicas

To produce better replicas of beta cells, Fussenegger and his colleagues took a closer look at the tightly choreographed rise and fall of chemical signals that cause stem cells to become mature beta cells during normal embryonic development. Then, the team created a genetic program to produce these chemical signals at just the right time, and inserted the program into a virus.

Next, they harvested fat from a 50-year-old woman and converted the fat cells into stem cells. Then, they inserted their genetic program, and coaxed the cells to become beta cells. Once the cells were mature, the viral DNA was gradually removed by ordinary cellular processes, so that no extra genetic material was left behind in the cells, Fussenegger said.

In a petri dish, the cells behaved much more like real pancreatic beta cells than previous reprogrammed stem cells had, the researchers reported Monday (April 11) in the journal Nature Communications.  

"The glucose responsiveness of those beta cells, which is the hallmark of beta cells, was practically identical to human islet cells that are used for transplantation," Fussenegger said.

Long road to a cure

The next step will be to find a suitable animal model to see if the cells work similarly in animals.

For people with type 1 diabetes, these cells would need to be encapsulated in a protective shield, such as a gel, so the immune system would not destroy them. For people with type 2 diabetes, the cells could be implanted as is, boosting insulin production and eliminating the main symptom of their disease, Fussenegger said.

The new technique is a "'Star Trek,' starship Enterprise kind of thing: designer genes, designer cells, synthetic switches," said Dr. Joel Habener, a physician and molecular endocrinologist at Harvard University who was not involved in the study. "It's pretty ingenious, I think."

The cells that the researchers made do an impressive job of producing insulin in response to glucose, or sugar concentrations, just as normal beta cells do, Habener said.

However, the cells still need to be tested in animals, such as mice, to make sure they are safe, Habener added. Then, the cells could be tested in human patients in five to 10 years, Fussenegger said.

Follow Tia Ghose on Twitterand Google+. Follow Live Science@livescience, Facebook & Google+. Original article on Live Science.

It may be possible to flip a chemical "switch" to turn on a feeling of fullness, a new study in mice suggests.

In the study, researchers found that a certain enzyme plays a role in how the brain responds to the hormone leptin, which normally signals that the body has consumed enough food and we should stop eating, according to the study, published in the journal Nature Communications on Monday (Feb. 29).

Leptin is a hormone that is released by fat tissue and binds to leptin receptors in the brain. Too much leptin, however, can lead to a condition called leptin resistance, in which the brain stops responding to leptin and therefore doesn't receive the signal to stop eating.  [8 Tips for Fighting Sugar Cravings]

Because leptin is secreted by fat tissue, the more fat tissue a person has, the more leptin is secreted. As a result, leptin resistance is common in obese individuals.

But enzymes in the body also appear to play a role in leptin resistance.

In the new study, the researchers found that an enzyme, called HDAC5, plays a role in the leptin pathway, according to the study. 

In the study, mice that could not make this enzyme were resistant to leptin, while mice that produced an excess of the enzyme were more sensitive to leptin. In addition, the researchers found that excess levels of the enzyme appeared to have a protective effect — that is, the mice with high levels of the enzyme did not gain as much weight as expected when fed a high-fat diet. 

More research is needed — whether the enzyme works the same way in humans is unclear.

But restoring "leptin sensitivity is an important step on the path towards sustainable weight loss and towards combating" diseases that can result from obesity such as Type 2 diabetes, Paul Pfluger, a neurobiologist at the Helmholtz Center Munich, a German Research Center for Environmental Health, said in a statement.

"In addition to the essential changes in diet and exercise behavior, in the future the individual components of the leptin [pathway] could be potential drug targets to support the weight loss process," Pfluger said.

However, he noted that it remains to be seen whether the enzyme will be a suitable target for fighting obesity in humans.

Follow Sara G. Miller on Twitter @SaraGMiller. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

A group of chemicals commonly used in cosmetics and other personal-care products may stimulate the growth of breast cancer cells at doses much lower than previously thought, a new study finds.

The study was done on human breast cancer cells growing in lab dishes, and it's unclear whether these chemicals, called parabens, act the same in the human body. But the chemicals have been shown in previous lab and animal studies to mimic the activity of the hormone estrogen, meaning they can bind to receptors in the body to which estrogen normally binds.This is a concern because when estrogen binds to estrogen receptors, it causes cells to multiply, and in women this increases breast cancer risk, said Dr. Dale Leitman, an adjunct professor of nutritional sciences and toxicology at the University of California, Berkeley, and the senior author on the study.

Parabens are a type of chemical preservative, and are found in a wide array of consumer products, including shampoos, body lotions and sunscreens.

It's also known that parabens can activate the same pathway as estrogen, but previous studies have found that they do so very weakly, Leitman told Live Science. "Because they're weak, they're assumed to be safe compounds," especially based on the levels of parabens that have been found in humans, he said. [What Is Estrogen?]

But previous studies looked at just the parabens by themselves, Leitman said.

"The real problem when you do studies in the laboratory is that you study one compound at a time, but in the body, that's not the case. What you're seeing in the body is really a combination" of the effects of many compounds, Leitman said.

In the new study, published today (Oct. 27) in the journal Environmental Health Perspectives, the researchers focused on the effects of parabens when mixed with one additional compound: a type of growth factor called heregulin that has also been linked to breast cancer cell growth.

In experiments, the researchers looked at how well the cells grew when they were exposed to both parabens and heregulin, compared with how the cells grew when exposed only to parabens. The scientists found that when they added heregulin, they could drop the level of parabens by 100 times and the cancer cells would still multiply faster than those without heregulin.

In other words, when the heregulin was added, the parabens were 100 times more potent at stimulating cancer cell growth compared with breast cancer cells exposed to only parabens.

With this increased potency, parabens may have an effect at a level that could be seen in humans, Leitman said.

Still, Leitman stressed that more studies are needed to determine the safety of the chemicals. Lab studies and animal studies are indirect ways of estimating the potential hazards of parabens, Leitman noted.

"All we can say from our study is that in order to determine how safe the parabens are … [we need] to test them not by themselves but with other chemicals that stimulate cell proliferation," he said.

Dr. Jiangang Chen, an assistant professor of public health at the University of Tennessee Knoxville who was not involved in the study, agreed.

"The study, like others published, only demonstrated the effects in the cells, which may not reflect the same scenario as in an intact biological system," Chen told Live Science. But additional studies have also indicated that other compounds may also contribute to how parabens affect breast cancer risk, Chen said.

Indeed, the study raises concerns that the "safe levels" of parabens used in cosmetic products should be re-evaluated, he said.

However, more research is ultimately required before a conclusion can be reached regarding the safety of parabens, Chen said.

Follow Sara G. Miller on Twitter @SaraGMiller. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

It's tough out there in the wild, especially for male howler monkeys. A new study suggests that these primates have to make a (evolutionary) choice: deep calls or small balls?

The smaller the size of the testes in a howler monkey species, the larger the size of the animal's hyoid bone, a structure that enables the monkeys to make deep, booming calls — noises on a par with those of a tiger, though howler monkeys are only about the size of cocker spaniels.

The relative sizes of the hyoid bones and testes appear to be related to how the animal lives and reproduces, according to a new study, published today (Oct. 22) in the journal Current Biology. Howler monkey males that live in groups with more than one male invest in larger testes, whereas those that live only with females invest in a booming, attractive voice.  [See Mug-Shot Photos of Howler and Other Monkeys]

Booming Calls

Curiosity about the howler monkey's booming calls dates back to at least Charles Darwin, who suggested that the males' cries are used to attract females, which choose mates based on the depth and resonance of these calls. (Females make calls, too, so howler monkey cries are not exclusive to mating rituals.) [Video: See a Howler Monkey Hoot]

Key to these calls is the hyoid bone, a structure that looks like a horseshoe in humans but is larger and more cuplike in howler monkeys. The bone creates a sort of resonance chamber that makes howler monkey hoots and hollers really ring out.

University of Utah anthropologist Leslie Knapp and her colleagues found that, in howler monkeys, male hyoid bones are up to five times larger than female hyoids, suggesting that Darwin was right in proposing a reproductive role for the monkeys' calls. Next, the researchers measured the size of hyoid bones across 10 species of these monkeys, which live in Mexico and Central America.

Making a trade-off

The results fit a "really exciting" pattern, Knapp told Live Science. The hyoids and testes varied widely across species: The species with the largest hyoids had bones 10 times larger than those with the smallest. And the largest testes were about seven times larger than the smallest testes.

Without exception, howler monkey species with larger testes had smaller hyoids and vice versa. And the anatomical differences showed no relation to environmental factors like food availability. Instead, they were linked to the monkeys' social structure.

Species living in a "harem" structure with one male mating with several females had larger hyoids and smaller testes. Species living with multiple males and females in a group, all mating with one another, had larger testes and smaller hyoids.

It's likely that the harem-heading howler monkeys use their deep calls to attract more females, or perhaps to scare off males that might steal their mates, Knapp said. As a result, they can get away with a lower sperm load — they compete for females before the actual mating act.

For male monkeys living with other males, though, the competition comes after copulation. A greater volume of sperm may give these monkeys a fertilization advantage in a female monkey that has mated with multiple males.

It's probably impossible for howler monkeys to evolve both a large hyoid and large testes, Knapp said.

"If they could, they would," she said. "I think, because they don't, it suggests that you can have one or the other, but you can't have both."

To really nail down the notion that monkeys make this reproductive trade-off, the researchers will have to look within species to see if large hyoids or large testes confer real advantages for males.

"We kind of have answered a question that Charles Darwin pondered in the 1800s, so that is exciting for us," Knapp said. "It also opens the doors to more questions, like what is going on within species? Is there evidence that males with the very largest hyoids are the ones having the most kids?"

The study also raises questions about what humans might have in common with their distant monkey cousins. In people, men with deeper voices are considered more attractive by women than men with higher-pitched voices, studies have found, but men with deeper voices don't have better-quality semen.

Children's hormone treatments may have planted the seeds for later Alzheimer's disease, according to a small, new observational study.

The study is based on the autopsies of eight people who died from the rare neurodegenerative disorder called Creutzfeldt–Jakob disease (CJD), which is caused by a prion, a type of misfolded protein. The eight patients were among hundreds of people inadvertently infected with the prion as children, between 1958 and 1985, when they received human growth hormone treatments intended to treat their short stature. These treatments were later realized to be contaminated with the prion.

Scientists found that four of the eight brains harbored extensive deposits of a protein called amyloid beta, which is the main component of amyloid plaque, the telltale characteristic of Alzheimer's disease.

Two more of the brains had patchy yet significant amounts of amyloid beta, and only one brain was completely free of the protein. Amyloid beta is not typically found in the brains of CJD patients.

The findings suggest that the same human growth hormone that was contaminated with a prion and caused CJD was also contaminated with amyloid beta "seeds," possibly because the people who donated the hormone had Alzheimer's disease, the researchers said. (Today, growth hormone is made in laboratories, but the original treatments used hormone that was taken from donors' pituitary glands after their deaths.)

The study also suggests that these amyloid beta seeds can be transmissible, spreading from person to person under certain circumstances and causing Alzheimer's symptoms, the researchers said in their study, published today (Sept. 9) in the journal Nature. [6 Foods that Are Good for Your Brain]

These patients' brains did not have the full-blown features associated with Alzheimer's disease, such as neurofibrillary tangles and the protein called tau. But the patients may have died before these elements could develop, said Dr. John Collinge of the United Kingdom's Medical Research Council, a senior author on the report.

"This is a highly unusual finding. We wouldn't have expected to see this Alzheimer's amyloid deposition in this age group," Collinge told reporters at a news briefing organized by Nature in advance of the study's release. The patients ranged in age from 36 to 51. "It's normally only seen in elderly individuals, unless you have a genetic predisposition to it, and none of these patients did."

The scientists stressed, however, that Alzheimer's disease is not contagious. Previous studies have shown, for example, that the disease cannot be transmitted through blood transfusions.

"I can imagine that this might result in a lot of misleading headlines," said David Allsop, a professor of neuroscience at the University of Lancaster in England, who was not involved in the study. "There is no evidence that Alzheimer's disease can be transmitted from one person to another, or through use of contaminated surgical instruments, and these results should be interpreted with a great deal of caution."

The situation that may have led to the transmission of the amyloid beta was unprecedented. Prior to 1985, thousands of children in North America and Europe who had growth problems were treated with human growth hormone collected from the pituitary glands of cadavers. Samples were pooled together, sterilized and collected into doses.

By 1985, it became clear that some doses were contaminated with the prion that causes CJD (the prion had been discovered in the 1970s), and the practice was halted. Today, hormones used for treatments are mostly manufactured using genetic engineering, in which hormone-producing genes are inserted into bacteria to produce large batches of the desired product.

Collinge speculated that cadavers from people with Alzheimer's disease may have had amyloid beta protein or precursory molecules in the pituitary gland. It will be difficult to test this hypothesis, however, because samples of the contaminated human growth hormone may no longer exist. [10 Things You Didn't Know About the Brain]

The finding is perhaps most alarming and relevant for the estimated 30,000 people who received human growth hormone treatments between 1958 and 1985. So far, hundreds of these people have died from CJD. Collinge said that these same patients might develop Alzheimer's disease in the decades to come if they were indeed infected with the amyloid beta seed.

"There will be more," Collinge said. "We know these diseases [CJD and Alzheimer's disease] can have extremely long incubation periods, 30 to 40 years."

Alzheimer's experts who were not associated with the study, however, downplayed this worry.

"While these findings are interesting and warrant further investigation, there are too many unknowns in this small, observational study of eight brains to draw any conclusions about whether Alzheimer's disease can be transmitted this way," said Dr. Doug Brown, director of research at the United Kingdom's Alzheimer's Society.

Moreover, scientists have emphasized that the new study cannot prove causation, i.e., that contaminated human growth hormone transmitted the amyloid beta seeds.

Given the importance of the finding if proven true, scientists will seek to replicate the results. France, like the United Kingdom, was hit hard by the hormone-contamination incident. Neuropathologist Charles Duyckaerts at the Pitié-Salpêtrière Hospital in Paris told Nature that his hospital has access to the remains of more than 20 patients who died from CJD, and he hopes to study their brains.

Meanwhile, Collinge, who directs the Prion Unit at the Medical Research Council, said his organization must remain vigilant in identifying others who may have been infected.

Follow Christopher Wanjek @wanjek for daily tweets on health and science with a humorous edge. Wanjek is the author of "Food at Work" and "Bad Medicine." His column, Bad Medicine, appears regularly on Live Science.

Caitlyn Jenner's very public transition from man to woman has raised awareness about the concept of hormone therapy for transgender individuals. Long-term hormone therapy is needed to create, and then maintain, the desired physical gender attributes — for Jenner, fuller breasts, curvier hips, thinner body hair and a higher-pitched voice.

But what makes transgender youth identify with a gender they weren't assigned at birth is not about having too many of the "wrong" hormones floating around, according to a study published this week in the Journal of Adolescent Health.

"We've now put to rest the residual belief that transgender experience is a result of a hormone imbalance," said Dr. Johanna Olson, of Children's Hospital Los Angeles. "It's not."

Olson and her colleagues found that transgender youth have sex hormone levels consistent with the gender they were assigned at birth. So, a transgender youth who is assigned a female gender at birth, usually based on the appearance of external genitalia, has the same female balance of estrogen and testosterone pumping through her body as any other biological girl; yet she nevertheless "feels" male. [10 Interesting Facts About the Female Body]

The report was part of a baseline analysis of 101 patients enrolled in a long-term study to determine the safety and efficacy of treatment that helps patients bring their bodies into closer alignment with their gender of identity. Some of these patients may be given hormone blockers to delay the onset of puberty, which otherwise would bring the development of unwanted sex characteristics.

The patients range in age from 12 to 24. On average, they first identified a discrepancy between their assigned gender and their self-perception of gender at about age 8. The patients come from diverse backgrounds in terms of race, income, family structure and religion, which argues against the idea that cultural influences would "make" them feel the way they do.

It may be that a transgender individual who feels male or female has a brain structure similar to those of other males or females, respectively, Olson said. However, the data remain inconclusive.

"I think that we will need a much larger body of research to reach conclusions about where gender identity lives in humans," Olson told Live Science. 

But searching for a biological explanation of gender identity shouldn't imply that being transgender is something that needs to be corrected. "The idea that being transgender is a 'disorder' of any kind invalidates a specific human experience that has existed since the beginning of human experience," Olson added.

Studies have revealed that transgender youth are three times more likely to have suicidal thoughts, and four times more likely to have attempted suicide, compared to nontransgender (also called cisgender) youth. These alarming statistics point to the distress that may arise from living in a society that's not accepting of the transgender experience.

"My goal is to move kids who are having a gender atypical experience from survive to thrive," Olson said. "With this study [now underway], we hope to identify the best way to accomplish that."

Follow Christopher Wanjek @wanjek for daily tweets on health and science with a humorous edge. Wanjek is the author of "Food at Work" and "Bad Medicine." His column, Bad Medicine, appears regularly on Live Science.

A 27-year-old woman in Belgium is now a mom after giving birth to a baby more than a decade after her ovarian tissue was removed and frozen, according to a new study.

The woman had her ovarian tissue frozen in her early teens, before she underwent a bone marrow transplant to treat her sickle cell anemia. Such transplants involve drugs that can destroy the ovaries.

The method that the researchers used to freeze the ovarian tissue could spare fertility in other girls who must undergo serious medical treatments during childhood, according to the study.

"Children are the patients who are most likely to benefit from the procedure in the future. When they are diagnosed with diseases that require treatment that can destroy ovarian function, freezing ovarian tissue is the only available option for preserving their fertility," Dr. Isabelle Demeestere, a gynecologist at the Erasmus Hospital at the Free University of Brussels, Belgium, and study co-author, said in a statement. 

Sickle cell disease

The woman was born in the Congo and was diagnosed at age 5 with sickle cell anemia, a sometimes deadly disease that prevents red blood cells from carrying enough oxygen to the body's tissues. She moved to Belgium when she was 11, and her sickle cell anemia progressively worsened. Soon after her move, it became clear she needed a bone marrow transplant.

However, such transplants require that a patient first undergo chemotherapy to wipe out the immune system and prevent it from attacking the new bone marrow. Chemotherapy also damages DNA, and thus can prevent the person's ovaries or testes from later producing eggs or sperm. Women who want to have children after chemotherapy can have their eggs extracted and frozen prior to treatment, but prepubertal girls do not yet have mature eggs that can be extracted.

Fertility-sparing operation

In this patient's case, doctors hoped to spare her fertility by removing her right ovary before she began her chemotherapy. They performed the procedure when she was about 13 — before she had begun menstruating, but after her breasts had developed (a sign that puberty was underway).

The bone marrow transplant was ultimately successful in treating the woman's sickle cell anemia, but her left ovary failed when she was 15. Afterward, she began taking hormone replacement therapy to initiate menstrual cycles.

Ten years later, the woman wanted to have a child. Doctors thawed some of her ovarian tissue, grafted four pieces onto what remained of her left ovary and 11 other pieces into her abdomen. She also stopped taking the hormone replacement therapy.

Healthy baby boy

Eventually, her transplanted ovarian tissue responded to the natural hormones circulating in her body, and developed follicles, which hold mature eggs. Two years after the transplant, she conceived a baby naturally, and gave birth to a healthy boy in November 2014.

The woman's case suggests that it is possible to preserve fertility in girls who have not yet reached puberty and must undergo treatments such as chemotherapy or radiation. [16 Most Unusual Medical Cases]

However, it’s not clear whether the same technique would be successful in younger children, as the girl had already started puberty when the operation was done, the researchers noted in the article, which was published today (June 9) in the journal Human Reproduction.

The ovarian tissue seems to be working normally, and it's possible that the woman could have another child using the same tissue, Demeestere said.

But even if the grafted ovarian tissue stops working, the woman is not out of options, the researchers said.

"She also has the possibility of undergoing a second transplantation with the remaining frozen tissue if the graft stops working, as we didn't transplant all the ovarian tissue the first time. We have another patient who became pregnant after ovarian transplantation, and she had two babies born after two graft procedures," Demeestere said.

Follow Tia Ghose on Twitter and Google+. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

Angelina Jolie Pitt underwent preventative surgery to remove her ovaries and fallopian tubes, according to the Op-Ed in the New York Times today that the actress, director and United Nations envoy wrote.

Two years ago, Jolie Pitt elected to have a preventative double mastectomy after learning that she had a mutation in the BRCA1 gene, a gene that codes for tumor-suppressing proteins, which normally repair damaged DNA.

"When someone has a harmful mutation in that gene, it no longer allows the cell to repair itself, and then the cells can go awry and become cancerous," said Dr. Marleen Meyers, the director of the Survivorship Program at the New York University Perlmutter Cancer Center, who was not involved with Jolie Pitt's medical care. [5 Things Women Should Know About Ovarian Cancer]

Breast and ovarian cancer are more prevalent among women with the harmful BRCA1 mutation. About 12 percent of women in the general population develop breast cancer, but up to 65 percent of women with a BRCA1 mutation develop the disease by age 70, according to the National Cancer Institute.

Likewise, about 1.4 percent of women in the general population develop ovarian cancer, but about 39 percent of women with a BRCA1 mutation develop it by the time they're 70 years old, the NCI reports.

What's more, Jolie Pitt's mother died of breast cancer at age 56, and the actress' aunt and grandmother also died of cancer, giving her a strong family history of the disorder, according to Jolie Pitt.

But she was aware of the risk, she writes. After her mastectomy, Jolie Pitt continued to get checked for ovarian cancer. One test she had monitored her levels of CA-125, a protein that tends to increase in women with ovarian cancer. But that test isn't very sensitive, and shouldn't be used by itself to detect early ovarian cancer, Meyers told Live Science.

"It's not a very good screening tool," Meyers said. "I appreciate that she was having it, but it's more a tool that's used once someone has ovarian cancer and they're getting treatment. Then it can be used to follow the progress of the treatment."

However, Jolie Pitt's doctors were also screening her levels of other inflammatory cells and proteins. These markers were elevated and possibly a sign of early cancer, her doctors told her.

It's likely that these markers were similar to CA-125, but are better at picking up earlier stages of ovarian cancer, Meyers said. Research into these markers is still in its early stages, but the results look promising so far, she said.

After a series of body imaging tests, including a CT and a PET, and a tumor test, Jolie Pitt learned that she did not have cancer. But she realized that it could still develop at any time, and her doctors helped her decide that removing her ovaries and fallopian tubes was a good option for her.

"To my relief, I still had the option of removing my ovaries and fallopian tubes and I chose to do it," Jolie Pitt wrote in today's (March 24) Op-Ed.

However, Jolie Pitt still has an increased risk of cancer. A harmful BRCA1 mutation can increase the risk of other cancers, such as colon cancer and melanoma. And the body also has ovarian-type cells in the abdomen, which can also become cancerous, Meyers said.

Jolie Pitt is "incredibly courageous," for sharing her experience, Meyers said. "I think it was being proactive and I think it's putting a beautiful face on genetic testing." It also brings attention to menopause, which Jolie Pitt will go through now that her ovaries are gone.

There was a surge in the number of women who requested preventative double mastectomies after Jolie Pitt made her first announcement in 2013, Meyers said. Women with the BRCA1 gene who are considering removing their fallopian tubes and ovaries can take Jolie Pitt's experience into account, but Meyers advised that women do what is best for their bodies, as surgery can carry risks of complications and infections.

"In women who carry the gene, it's a reasonable thing to consider and talk about, but it's still a decision that needs to be made one-on-one" with a doctor, Meyers said.

Follow Laura Geggel on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

Pancreatic cancer affects a small organ behind the stomach that produces hormones and digestive juices for the body. It is the number-four cause of cancer deaths and most often affects individuals over the age of 65. It is estimated there were 46,420 new cases of pancreatic cancer and 39,590 deaths in the United States in 2014, according to the National Cancer Institute. 

Symptoms & causes

There are two types of cancer that affect the pancreas: adenocarcinoma and endocrine cancer. Adeonocarcinomas grow in ducts where digestive juices are made. Most pancreatic cancers are of this type. Endocrine cancers develop in pancreatic cells that release hormones, such as insulin.

Symptoms of pancreatic cancer often remain absent until the disease has progressed to an advanced stage. At that time, individuals may notice a condition called jaundice in which the skin yellows.

The yellow color indicates that the pancreas has interfered with the liver, said Dr. Sameh Mikhail, an assistant professor of oncology at The Ohio State University Wexner Medical Center. 

"The pancreas is very close to the liver, so many times it blocks the digestive juices that the liver produces that are intended to reach the small intestine," Mikhail told Live Science. "When it blocks the digestive juices, they back up into the blood. They have a yellow bile in them, so it gives patients a yellow color."

People may also lose weight, have increased heartburn and feel pain in their abdomen and back. Depression may occur.

Both types of pancreatic cancer develop as a result of genetic mutations. Family history, as well as acquired or inherited genetic mutations such as a mutation in a gene called BRCA2 (also a risk factor for breast cancer), can increase the risk of developing pancreatic cancer. Old age, obesity, diabetes and smoking are also risk factors.

Diagnosis & tests

Often pancreatic cancer is not diagnosed until it has spread beyond the pancreas. Still, early diagnosis does not necessarily improve prognosis since pancreatic cancer grows very quickly.

Several tests exist to diagnose and "stage" pancreatic cancer. Ultrasound, computerized tomography (CT) scan and magnetic resonance imaging (MRI) allow a physician to visualize the location and size of a tumor.

Endoscopic procedures may be employed to see inside the pancreas. These include endoscopic retrograde cholangiopancreatography (ERCP) and endoscopic ultrasound (EUS). In ERCP, a physician inserts an endoscope — a bendable tube with a camera attached at the end — and pushes it down the throat into the small intestine. Next, a catheter is inserted into the endoscope and passed down into the small intestine. The physician then releases dye from the catheter that will illuminate the pancreatic ducts in an X-ray.

In an endoscopic ultrasound, the physician uses an endoscope to move an ultrasound device into the stomach where it creates images.

A biopsy, in which tissue from the tumor is removed for testing in the lab, is typically required to confirm diagnosis. A biopsy may be performed with a needle through the skin or through an endoscopic ultrasound.

Finally, blood tests can help physicians determine how far along the cancer has progressed. For instance, doctors can look for the tumor marker CA 19-9. 

"When the cancer grows, it releases that protein into the blood," Mikhail said. "But it's important to emphasize that it is not definitive, because occasionally CA 19-9 can be elevated in absence of a cancer. And in other situations, patients may have a cancer, but would have a normal CA 19-9."

Pancreatic cancer may exist in one of four stages. In Stage I, the cancer is still limited to the area of the pancreas. In Stage II, the cancer can be found just outside the pancreas. By Stage III, cancer cells have metastasized to blood vessels and lymph nodes, and in Stage IV it has moved to other organs.

Treatment & medication

Treatment options depend on the stage of the cancer. According to the National Cancer Institute, pancreatic cancer is only potentially curable if it is diagnosed before it has spread beyond the organ. At that stage, it is possible that surgery can remove the entire tumor.

Surgeons may try to remove the tumor if the cancer is not surrounded by blood vessels. "If major arteries are involved, it's very hard to remove the cancer," Mikhail said. 

If surgery is an option, people should ensure that their surgeon or surgery team has ample experience in removing pancreatic cancer, he added. 

Radiation and chemotherapy are commonly given following — and sometimes before — surgery to ensure that any remaining cancer cells are destroyed. If surgery is not an option, radiation and chemotherapy may be given as the sole treatment.

Chemotherapy drugs for pancreatic cancer are administered through an I.V. Although they can be effective at killing cancer cells, they also destroy some healthy cells, which can cause side effects such as hair loss and nausea.

Five years ago, people with stage 4 pancreatic cancer lived a medium of six months after starting treatment . Now, with two new chemotherapy regimens — FOLFIRINOX and gemcitabine and albumin-bound paclitaxel — people with stage 4 cancer live a medium of 11 months after starting treatment.

"This has been a tremendous breakthrough in the treatment of pancreas cancer," Mikhail said, though he added that it "still leaves a lot of room for improvement."

Often, drugs aimed at particular aspects of cancer cells may be included in the treatment regimen. Called “targeted therapy”, these drugs include growth factor inhibitors such as erlotinib and anti-angiogenesis factors. Anti-angiogenesis factors prevent the tumor from forming blood vessels that are required for the tumor to grow. These drugs are still in clinical trials for use in pancreatic cancer.

Alternative therapies may help individuals cope with a cancer diagnosis, as well as the stress of the treatment process. Types of alternative treatments include art and music therapy, meditation and exercise such as yoga.

Prevention

Imaging and genetic tests may be used to screen people who have a family history of the disease. For example, there is a genetic test that looks for alterations in a gene called K-ras that is related to cell growth. According to the American Cancer Society, however, these tests are only currently recommended for high-risk people.

As researchers begin to better understand the process from genetic mutation to cancer development, it may one day be possible to develop better screening methods that are available to the general population, and can diagnose pancreatic cancer earlier.

Additional reporting by Live Science Staff Writer Laura Geggel. Follow her on Twitter @LauraGeggel. Follow Live Science @livescience, Facebook & Google+.

Additional resources

• Learn about the pancreas and what it does at Johns Hopkins Medicine.
• Symptoms are subtle and hard to notice. Familiarize yourself with the signs of pancreatic cancer at the National Institutes of Health. 
• Supreme Court Justice Ruth Bader Ginsburg had surgery to remove her pancreatic cancer, according to the New York Times.

The children of women who are exposed to higher levels of chemicals called phthalates during pregnancy may have lower IQ scores than those whose mothers are exposed to lower levels of those chemicals, according to a new study. Phthalates are common in products such as plastics and the fragrances used in shampoos, air fresheners and dryer sheets.

In the study, researchers followed 328 women in New York City who were either African-American or Dominican-American, as well as their children, who were born between 1998 and 2006. The researchers measured the levels of four types of phthalates in the women's urine, and looked at the children's IQ scores at age 7.

They found that the children of mothers with the highest urine levels of two chemicals — called di-n-butyl phthalate (DnBP) and di-isobutyl phthalate (DiBP) — had IQ scores that were about 6 to 8 points lower than those of the children whose mothers had the lowest levels of those chemicals in their urine.

The findings are important because "shifts in IQ during these school-age years might have influences later on educational attainment and occupational choice for the children," said study author Pam Factor-Litvak, an associate professor of epidemiology at Columbia University's Mailman School of Public Health. [12 Worst Hormone-Disrupting Chemicals]

The researchers also found a link between the levels of those chemicals and specific aspects of IQ, such as the speed at which kids processed information, their ability to understand nonverbal information and their short-term memory.

One strength of the study was that it followed the participants over time, said Dr. Susan Klugman, director of reproductive genetics at Montefiore Medical Center in New York, who was not involved in the research.

"But I do feel that environmental toxin studies are tough, only because there are so many factors involved," and child development studies depend on the population being studied and are not always applicable to other groups, Klugman told Live Science.

The researchers noted that their findings show an association, but not a cause-and-effect link between prenatal exposure to the chemicals and lower IQ scores. However, the researchers did find consistent associations between the two.

"Before we can make any absolute conclusions about causality, a study of wider population would be helpful, for sure," said Dr. Kenneth Spaeth, director of occupational and environmental medicine at the North Shore-LIJ Health System in New York, who was not involved in the study. "I think a study like this certainly raises concerns and puts the level of concern about this much higher for everyone, not just for this population that was studied."

There may be several mechanisms behind the link between prenatal exposure to certain phthalates and children's IQ, Factor-Litvak said. First, phthalates disrupt the body's hormones, so they may affect brain development, she said.

"They may also modulate the activity of an enzyme called aromatase," which converts testosterone into estrogen, a hormone that is very important in brain development, Factor-Litvak told Live Science. Phthalates may also interfere with the production of thyroid hormone, which is a major player in the timing of brain development, she said.

Moreover, the chemicals may also disrupt the brain's activity related to the neurotransmitter dopamine, "which is linked to inattention and hyperactivity," Factor-Litvak said.

"They [the mechanisms] are not exclusionary," she said. "More than one could be going on at the same time." All of these mechanisms have been hinted at in animal studies of phthalates, she added.

To reduce the potential harmful effects from exposure to phthalates, the researchers recommended that people avoid microwaving food in plastic, and they discouraged consumers from using scented personal products. They also advised against using recyclable plastics labeled as 3, 6 or 7, which contain the chemicals, and encouraged people to start using glass containers instead of plastic ones.

When it comes to products labeled as "phthalate-free," it is not clear whether the chemicals that are used instead of phthalates are safer for health, because they have not been studied yet, Factor-Litvak said.

The use of certain phthalates in toys for young children has been banned, but there is no legislation that might affect exposure to the chemicals during pregnancy, "which is likely the most sensitive period for brain development," Factor-Litvak said. Moreover, product labels are not required to specify whether a product contains phthalates, she added.

"There is almost nothing in the world that is entirely risk-free or even toxin-free," Spaeth told Live Science. "I have never heard any public health advocates calling for the elimination of plastics. But I think most would agree that we could do a much better job in changing the ingredients used in products to an extent that would certainly put us at lower risk for exposure to phthalates and BPA [bisphenol-A], and other kinds of chemicals as well." [5 Ways to Limit BPA in Your Life]

Absent regulations, expecting mothers should pay attention to their exposure to these chemicals, Klugman said.

"There are so many environmental toxins, and I do think that pregnant women and parents have to limit prenatal and postnatal exposure, or attempt to limit it," Klugman said. "People can't live their life totally in fear, but I think we have to take a step back and think about what we do, think about what we do when we are pregnant, think about what we expose our children to," Klugman said.

The study was published today (Dec. 10) in the journal PLOS ONE.

Follow Agata Blaszczak-Boxe on Twitter. Follow Live Science @livescience, Facebook & Google+. Originally published on Live Science.

Landon Jones is a 12-year-old boy with a very unusual condition: He never gets hungry or thirsty.

The boy, of Cedar Falls, Iowa, noticed something was wrong when he woke up on Oct. 14, 2013, feeling dizzy and suffering from chest congestion. A chest X-ray later showed he had a bacterial infection in his left lung, which later healed.

But ever since that day, according to The Des Moines Register, Landon has had no desire to eat or drink, even though he can still taste and smell normally. Landon's weight has dropped from 104 lbs. (47 kilograms) to a mere 68.4 lbs. (31 kg), and his parents say they have to constantly remind him to eat and drink. [16 Oddest Medical Cases]

The boy has had medical tests and doctor's appointments in five cities, in attempts to find the cause of his bizarre condition. He has undergone a spinal tap, brain scans, abdominal imaging, and nutritional and psychiatric evaluations, but doctors have been unable to diagnose the problem.

"This is exceedingly unusual. I've never heard of a case like this," said Dr. Ashesh Mehta, director of epilepsy surgery at the North Shore-LIJ Comprehensive Epilepsy Care Center in Great Neck, New York, who was not involved in the boy's treatment.

Hunger and thirst in the brain

Hunger and thirst are part of a larger circuit controlled at many different levels in the brain, Mehta told Live Science. A problem anywhere along this circuit could cause Landon's symptoms, he said.

Dr. Marc Patterson, a pediatric neurologist at the Mayo Clinic in Rochester, Minnesota, who has been treating Landon, told the Register that there may be a problem with Landon's hypothalamus, a small, pea-size region at the base of the brain that controls hunger, thirst, body temperature, sleep and other vital functions.

It could be that the bacteria that infected Landon's lung crossed the blood-brain barrier — the selectively permeable membrane that separates the body's circulatory system from the brain — and affected his hypothalamus. An infection or lesion of this brain area could explain why Landon feels neither hunger nor thirst, doctors say.

"It makes sense that the two go hand in hand, because hunger and thirst are both controlled by the hypothalamus," said Dr. Caroline Messer, an endocrinologist at Lenox Hill Hospital in New York City.

But another possibility is that Landon has developed a resistance to the hormone ghrelin, which stimulates hunger, or now has an overproduction of the hormone leptin, which causes feelings of satiety. But these would explain only the loss of appetite, not the lack of thirst, Messer told Live Science.

Eat, drink, eat

Even though Landon's parents constantly remind him to eat, he is still losing weight, the Register reported. If he can't ingest enough calories by eating, doctors said they may have to install a feeding tube.

But such tubes are prone to infection, and carry a high risk of complications, Messer said. Instead, Landon might benefit from a drug called megestrol acetate (brand name Megace), an appetite stimulant often given to cancer and AIDS patients, she said.

Landon's inability to feel thirst could also upset his body's electrolyte balance, and his sodium levels could become too high if not monitored, Messer said.

Landon's case may be the only one like it in the world, his doctor told The Register. His family has contacted a division of the National Institutes of Health that evaluates and treats patients with rare, undiagnosed diseases. The program invites only 50 to 100 patients to its Bethesda, Maryland, campus each year to be evaluated by a team of specialists, according to CBS News, and Landon hopes to be one of them.

"One would hope he'll outgrow this," Mehta said. "But for now, [Landon's family] will have to keep a close eye on calorie intake."

Follow Tanya Lewis on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Ovarian cancer occurs when cells in one or both ovaries proliferate out of control. Although women of all ages are susceptible to ovarian cancer, around half of those that are diagnosed are age 63 or older, according to the American Cancer Society. It also notes that in the past 20 years, incidence went down by 1% to 2% per year from 1990 to mid-2010s, and by almost 3% per year from 2015 to 2019. Death from ovarian cancer also declined from 2% annually during the 2000s and early 2010s, to more than 3% annually from 2016 to 2020.

There were an estimated 19,880 new cases and about 12,801 deaths from ovarian cancer in the United States in 2022, according to the National Cancer Institute. 

A woman's chances of getting ovarian cancer in her lifetime sit at around 1 in 78, with the lifetime chance of dying from the disease at around 1 in 108, according to the American Cancer Society.

Ovarian cancer is rare, but it's the fifth most frequent cause of cancer death in women in the United States, said Dr. David Cohn, a gynecologic oncologist and the chief medical officer at The James Cancer Hospital and Solove Research Institute. The disease is usually discovered late in its progression, which makes it more dangerous, he said.

"The reason why many women end up dying of it is that it tends to be picked up [by doctors] later in the course of the disease, rather than early," Cohn said. "Otherwise, [it would] be very curable."

Types of ovarian cancer

There are three main types of ovarian tumors. The most common type — epithelial tumors — happens to the cells on the surface of the ovary, and it accounts for about 90% of malignant ovarian tumors, according to Cancer Research UK. 

Less common are germ cell ovarian tumors, which occur in the egg-producing cells of the ovary, often in women younger than 30 years of age. 

The other type consists of sex cord-stromal ovarian tumors, which occur in the ovary cells that release female hormones, said Cohn.

Risk factors for ovarian cancer

The disease has several risk factors, including increased ovulation, Cohn told Live Science.

"Women who have ovulated more, which means they've never been pregnant and never breast fed, and haven't taken birth control pills, have a higher chance of the disease compared to those who have been pregnant, breast fed and taken birth control pills," he said. 

Similarly, fertility medications that cause women to ovulate more frequently have been implicated as a risk factor for the disease, Cohn said. 

Genetics also plays a role. Up to a quarter of all ovarian cancers are linked to genetic changes that predispose women to develop the cancer, Cohn said. For example, mutations in the BRCA genes (BRCA1 or BRCA2) are tied to ovarian cancer. 

Women of European Jewish ancestry, known as Ashkenazi women, and Icelandic women have a higher chance of having a mutation in one of the two BRCA genes, Cohn said. 

What are the symptoms of ovarian cancer?

Overall, many women with ovarian cancer have no symptoms or just mild symptoms until the disease is in an advanced stage and hard to treat, Cohn said. For that reason, it also has the highest mortality of all cancers of the female reproductive system, according to the National Institutes of Health (NIH).

Although some ovarian cancer patients experienced symptoms such as abdominal pain, bloating, unexplained back pain and abnormal vaginal bleeding, a 2010 study in the Journal of the National Cancer Institute found that these relatively nonspecific symptoms may not definitively point toward ovarian cancer. Doctors would have to evaluate 100 women with these symptoms to come across one case of ovarian cancer. 

Other symptoms include quickly feeling full when eating, unexplained weight loss and even changes to bowel movements, according to the Mayo Clinic.

There is a push to educate both doctors and the public that when women experience several of these symptoms together, such as increases in urinary frequency, nausea and pelvic pain, it may indicate that they are at risk for ovarian cancer.

"The current thinking is that when women have these symptoms that go together, and that they don't go away or that they worsen over time, then that may be a problem," Cohn said. 

How is ovarian cancer diagnosed?

There is currently no standardized screening test available for reliably detecting ovarian cancer, Cohn said. If a woman reports feeling symptoms of ovarian cancer, the doctor may perform a pelvic or abdominal exam to see whether a mass or lump is present. An ultrasound or CT scan can also help determine whether the patient has an unexplained ovarian growth. 

If there is a mass present, the doctor may order a CA125 test, which screens for a tumor-associated protein present in the blood. The test is not good at detecting ovarian cancer in the general population, but it's helpful when indicating whether a woman with a known lump may be at risk for the disease, Cohn said. 

A CA125 screening program of 22,000 postmenopausal women detected 11 out of 19 cases of ovarian cancer, for an apparent sensitivity of 58%. Of that, only three out of those 11 cases were at stage I.

If the above tests do not rule out ovarian cancer, doctors would then proceed to do a laparotomy, which is a slightly less invasive surgical procedure, according to the Mayo Clinic. The surgeon may remove a tissue mass or abdominal fluid to determine whether there's a cancerous growth.

A pap test may be an effective way to screen for cervical cancer, but it does not screen for ovarian cancer.

Treatment for ovarian cancer

Standard treatments for ovarian cancer include surgery, where much of the tumor and the affected tissues are removed. Radiation therapy and chemotherapy may also halt cancer progression by killing the cancer cells or keeping them from dividing, according to the National Cancer Institute. These treatments could be administered before or after surgery. 

Novel treatments currently under investigation include new chemotherapy drugs, vaccines, gene therapy and immunotherapy, according to the Mayo Clinic.

Women with ovarian cancer should seek care from gynecologic oncologists, who specialize in ovarian cancer. That specialized training is necessary to ensure the effectiveness of the treatment, Cohn said. "Compared to those that have the correct operation or an operation that fully removes the cancer, inadequate surgery leads to a worse survival," he said.

Many cancer treatments can have adverse side effects. For example, bevacizumab (sometimes referred to by its brand name Avastin) works by disrupting the blood supply to the tumor, possibly causing the growth to shrink. Yet gastrointestinal perforation, a serious medical condition that happens when a person develops a hole in their esophagus, stomach, small intestine, large bowel, rectum or gallbladder, is significantly increased for those who take the drug, according to a 2009 review published in Lancet Oncology that studied 12,294 patients. 

As for chemotherapy, side effects such as abdominal pain, nausea and vomiting may prevent many women from completing a full course of treatment, according to the Mayo Clinic.

Some women are considered at high risk for ovarian cancer; for instance, those with a first-degree relative (like a mother, daughter or sister) who have been diagnosed with the disease are considered at high risk. These women might consider aggressive preventative measures such as prophylactic oophorectomy, where both ovaries are removed in hopes of preventing the onset of ovarian cancer. 

Additional resources

• Learn more and find support at the American Cancer Society.
• The National Ovarian Cancer Coalition helps raises awareness about the disease.
• Get the latest news about clinical trials, statistics and research at the National Cancer Institute.

A new "do-it-yourself" ultrasound method could let women who are undergoing in vitro fertilization (IVF) cut down on their trips to the doctor's office, a new study suggests.

The technology allows these women to perform vaginal ultrasounds at home, while their doctor views the results from afar.

During IVF treatment, women are given hormones that trigger their ovaries to produce multiple eggs in one cycle. But although the hormone injections can be done at home, women need to visit the doctor frequently — sometimes five or six times over a two-week period — to monitor how well the treatment is working. They are given a vaginal ultrasound (in which an ultrasound probe is placed into the vagina) to view the ovaries, so the doctor can see whether the eggs are maturing.

The new study suggests it may be possible for women to perform these ultrasounds on themselves, at home. [Future of Fertility Treatment: 7 Ways Baby-Making Could Change]

In the study, 123 women in Belgium who were undergoing IVF were randomly assigned to either home monitoring, or the regular trips to the doctor's office. In the home monitoring group, women were given a laptop with imaging software and a vaginal probe with a USB connection. They were shown how to use the probe to take video recordings of their ovaries, and how to upload and send the videos to their doctor.

After taking an initial sonogram, women in the home monitoring group did not need to visit the doctor until their eggs were ready to be collected, while those in the regular care group made several doctor's visits.

Women in both groups had similar outcomes in terms of the number of eggs that doctors were able to retrieve and the number of fertilized eggs they were able to have implanted. About one-quarter of women in both groups became pregnant.

And because women in the home monitoring group made fewer doctor's visits, they spent less money on transportation, and took less time off of work. Patients in the home monitoring group were also more satisfied with their treatment.

"Home monitoring … may provide a patient-centered alternative to the standard methods," the researchers, from Ghent University Hospital in Belgium, wrote in the July 3 issue of the journal Human Reproduction. "This approach offers several advantages for patients as well as care providers, including similar results to the traditional methods … and potentially bringing care to patients in poor resource settings."

The technology used in the study has been licensed to a company called Fertihome in Europe, and an affiliated company called Sonaura in the United States. The product is being used in about five centers in Europe, and Sonaura is currently seeking approval from the U.S. Food and Drug Administration to sell the product in the United States, said Patrick Bols, who represents Sonaura.

Bols said the product saves women time — some women who live far away from a fertility center have to travel hours just for a 2-minute sonogram, he said.

However, experts were skeptical about how widely home ultrasounds would be used in the United States.

Dr. Tomer Singer, a reproductive endocrinologist at Lenox Hill Human Reproduction fertility clinic in New York City, said that medicine in general is moving toward telemonitoring (using technology to monitor patients remotely), and that techniques for home monitoring will continue to evolve in the future.

But Singer said he would like to see more research on how the home monitoring technique fares in women who are at increased risk of developing painful and swollen ovaries as a side effect of the hormone drugs — a condition known as ovarian hyperstimulation syndrome. (One of the reasons that vaginal ultrasounds are performed is to prevent this syndrome.)

"I'm all in favor of doing monitoring at home; I just don't think that this study proves that doing it in all patients is feasible," Singer said.

In addition, he noted that many patients want the guidance medical professionals provide during office appointments — for instance, to tell them how well their treatment is working, and answer their questions. "If I were to give them [my patients] this option, I think less than 20 percent would chose that route," Singer said.

Dr. Avner Hershlag, chief of the Center for Human Reproduction at North Shore University Hospital in Manhasset, New York, agreed and said he felt American patients — who often have to pay for IVF treatment out-of-pocket — would have anxiety about doing the procedure themselves. "For them to feel that they can rely on their own monitoring, I think, is a big leap," Hershlag said.

Hershlag said that some clinics offer early-morning and late-evening appointments so that women don't have to miss work. Still, with more research, Singer said he thought certain groups of women could benefit from home monitoring, including those who live far away from their fertility clinic, those who've undergone IVF previously and those who are uncomfortable with a nurse or doctor inserting a vaginal probe.

Follow Rachael Rettner @RachaelRettner. Follow Live Science @livescience, Facebook & Google+. Original article on Live Science.

Unlike female nipples, male nipples appear to be purely decorative. But can they also be functional and secrete milk — that is, can men lactate?

Short answer: Yes, under certain circumstances.

To start, male lactation has been observed in a few domesticated animals, including cats, goats and guinea pigs, on rare occasions. However, male lactation seems to be common only in dayak fruit bats, though it's not yet clear why males of this species have the biology to spontaneously produce milk.

Importantly, human biology also makes male lactation a possibility.

For both women and men, breast tissue contains hollow cavities called alveoli, which are lined with milk-secreting cells. But the critical determinant of lactation is prolactin, a hormone that's produced by the pituitary gland and stimulates the mammary glands to produce milk. [11 Surprising Facts About the Endocrine System]

Normally, non-pregnant women can have almost double the amount of prolactin circulating in their body than men, according to the National Institutes of Health. This concentration can spike by nearly tenfold during and after pregnancy.

Research has shown that male prolactin levels can also surge, according to a 2008 review on male lactation published in the journal Trends in Ecology and Evolution.

For instance, scientists documented lactation in male WWII prison camp survivors, who had suffered months of starvation. After receiving adequate nutrition, their hormone-producing glands rebounded far quicker than their livers (which normally metabolize hormones), resulting in hormonal spikes that caused lactation.

Similarly, a condition called liver cirrhosis can cause lactation by disrupting the organ's normal, hormone-metabolizing function.

Health issues that affect the pituitary gland or the hypothalamus, which normally inhibits the release of prolactin, can also cause male milk production.

For example, a 2010 study published in the Canadian Medical Association Journal documented lactation in a man with a pituitary tumor.

Follow Joseph Castro on Twitter. Follow us @livescience, Facebook & Google+. Originally published on Live Science.

Marriage is linked with numerous health benefits that simply cohabiting doesn't seem to provide. Now, research suggests the reason why — the brain links "just" living together with a lack of commitment and can't relax.

The new study used functional magnetic resonance imaging (fMRI) to examine the brains of cohabitating and married heterosexual couples, as well as same-sex couples, half of whom considered themselves married despite lacking legal recognition. The findings revealed that parts of the brain are less reactive to stress when somene is with a person they consider themselves married to. 

"We really pay close attention to when it's safe to let down our guard and to outsource our stress response to our social networks," said study researcher Jim Coan, a psychologist at the University of Virginia. [I Don't: 5 Myths About Marriage]

The findings were unexpected, Coan added: "I'm sort of freaking myself out with this research."

The marriage benefit

In a study published in 2006, Coan had found that when threatened with a mildly painful electric shock, married women had a decreased brain response to the threat when holding their husband's hand versus a stranger's, or no hand at all.

The effect occurred in the hypothalamus, an almond-sized structure buried deep in the brain that helps regulate some of the body's responses to stress, including increased blood pressure.

The finding hinted at why marriage is linked with physical health, Coan said. But there were only 16 participants, all married women.

"We really needed to replicate the findings," he said.

In the new study, Coan and his colleagues not only replicated the findings, they expanded them. This time, they studied not only married couples, but also couples who were cohabiting. Most crucially, they were able to recruit 26 same-sex couples to participate in the experiment. [5 Myths About Gay People Debunked]

Gay marriage is not legal currently in Virginia, so none of the same-sex couples were married. However, half of the couples considered themselves married and described themselves as such to friends, family and acquaintances. The other half said they were just living together.

Facing it together

All of the couples went through the same experimental procedure: One person would lie in the fMRI scanner, where they could see a computer screen that cued them into a potential threat — a shock on the ankle. Some cues signaled a 20 percent chance that a shock was coming, and others signaled a 0 percent chance of shock.

During this process, the volunteers either held their partner's hands, a stranger's hands, or faced the shocks alone.

Again, the study found that when married couples held hands, the hypothalamus of the person threatened with the shock calmed down compared with when they held hands with a stranger or no one. Surprisingly, though, the same effect held true for same-sex couples who considered themselves married — even though they were not legally different than the same-sex couples who considered themselves to be cohabiting.

"There's a pretty strong and predictable regulation effect in the married couples and no regulation at all in the cohabiting couples," Coan said. "None, zero."

In your head

The married and cohabiting couples were matched on the length of their relationship and relationship satisfaction, Coan said. The key difference seems to be how people think of their relationship. 

"When you're asserting, in the same-sex couples, 'We're just living together, we're only living together' it means you haven't really committed," Coan said. "It means that you're explicitly maintaining a little bit of emotional distance. You're not locked in. I think that's just enough to signal to your brain that you can't outsource your stress response to your partner."

In other words, people who hold back on commitment don't fully trust their partner has their back, the study suggests.

There may be benefits to cohabiting, Coan said — at the very least, it's cheaper for two adults to live together versus separately, which has its upsides. But the bar for emotional benefits seems to be higher, he said.

However, as the same-sex couples show, the marriage benefit may not be about the legal or religious recognition; rather, thinking of oneself as fully committed is key.

"Marriage is a proxy for trust and reliability," Coan said.

A cohabiting couple could recognize the benefits of marriage without the marriage license, Coan said, but it's less likely given that people who choose cohabitation over marriage are making the choice not to be locked in.

Marriage, Coan said, is "a socially understood sanctioned world that communicates to your partner commitment, really powerful, strong commitment, the kind of commitment that is hard to get out of. That's what your brain is looking for."

Coan will present the research today (Feb. 14) at the annual meeting of the Society for Personality and Social Psychology in Austin, Texas.

Follow Stephanie Pappas on Twitter and Google+. Follow us @livescience, Facebook & Google+. Original article on Live Science.

Pregnant women exposed to phthalates, a group of hormone-mimicking chemicals found in personal care products and processed foods, may have an increased risk of preterm delivery, a new study suggests.

The study included 130 women in the Boston area who had given birth early, before 37 weeks of pregnancy, and 352 women who delivered at full term between 2006 and 2008. The researchers measured the levels of common phthalates such as DEHP in the women's urine up to three times during their pregnancies.

They found that women who had the highest levels of phthalate metabolites in their urine had a risk of preterm birth that was two to five times higher when compared with women who had the lowest levels.

What's more, when the researchers looked only at the 57 women who had "spontaneous preterm delivery," meaning they didn't have a medical condition that could explain their early delivery, they found the link between exposure to phthalates and risk of preterm delivery was stronger, according to the study published today (Nov. 18) in JAMA Pediatrics.

"These data provide strong support for taking action in the prevention or reduction of phthalate exposure during pregnancy," the researchers wrote in their findings.

Phthalates are chemicals widely used in making flexible and durable plastics, and many other products such as adhesives, detergents, soaps, shampoos, hair sprays, perfumes and deodorants. People are exposed to these potentially hormone-disrupting chemicals through contact with phthalate-containing products, and eating certain processed and canned foods. [12 Hormone-Disrupting Chemicals & Their Health Effects]

"For women who are interested in reducing their exposure, reducing use of personal care products, buying phthalate-free [products] when possible, and eating fresher foods may help, although research on that is limited," said study researcher John Meeker, an associate professor of Environmental Health Sciences at University of Michigan School of Public Health.

Preterm birth, defined as the birth of an infant before 37 weeks of pregnancy, is a leading cause of death or long-term neurological disabilities in children. The rate of preterm birth in the United States has increased by more than a third between 1981 and its peak at 12.8 percent in 2006. The rates slightly decreased in the subsequent years, to about 11.5 percent in 2012, which means one out of every eight children is now born prematurely, according to the Centers for Disease Control and Prevention (CDC).

A recent review of studies looking for what might underlie the increase in preterm birth rates identified risk factors such as increasing maternal age and use of assisted reproduction. However, nearly half of the increase remains unaccounted for, said Shanna Swan, a professor of preventive medicine at Icahn School of Medicine at Mount Sinai, New York.

The new study provides "strong evidence that environmental chemicals, and phthalates in particular, likely contribute significantly to that unknown and other category," Swan wrote in an editorial published along with the new study.

The study showed an association, not a cause-and-effect relationship, between phthalates and preterm birth. However, there are reasons to think phthalates could cause preterm births; for example, phthalates may cause inflammation in the uterine lining, the researchers said.

Lab studies have shown that phthalates can cause inflammation, but this needs to be studied in humans. Other ideas about possible mechanisms by which phthalates affect pregnancy involve women's immune response, oxidative stress, and hormone disruption.

"There's a list of things phthalates have been shown to do in experimental studies. Much work is left to be done in human observational studies," Meeker told LiveScience.

Other factors that contribute to higher risks of preterm delivery include smoking, drinking, infection, stress and high blood pressure during pregnancy. A study published in January 2013 in the journal Lancet predicted that current interventions to address known risk factors would decrease preterm birth rates by only 5 percent by 2015.

Exposure to phthalates may be one risk factor that could be prevented by behavioral modification or through policies aiming at reducing the use of phthalates, the researchers said.

Email Bahar Gholipour. Follow LiveScience @livescience, Facebook & Google+. Original article on Live Science.

Environmental Working Group, an organization that advocates against the use of toxic chemicals, has released a list of the 12 worst hormone disrupting chemicals.

Here is our breakdown of the list, which includes information from Environmental Working Group (EWG) and other sources:

Bisphenol A (BPA)

This chemical is found in many products, including canned foods, plastics, and dental sealants, and is similar in structure to the hormone estrogen. Studies have linked BPA exposure with many health problems, including obesity, early puberty and miscarriage. However, these studies only show associations, and cannot prove that BPA exposure actually causes these conditions. Whether levels of BPA in the environment are harmful to people is still being studied.

Dioxin

These are long-lived chemicals that are widely found in foods, and accumulate in animal fatty tissue, according to the World Health Organization. They have been linked to lower sperm count and other reproductive system effects, according to EWG. Chronic exposure to dioxins has been linked to immune system problems and cancer. But while the chemical is known to be toxic at high levels, "background" exposure (exposure to normal levels in the environment) is not expected to affect human health on average, WHO says.

Atrazine

This commonly used pesticide can contaminate drinking water, EWG says. In animal studies, it has been linked to tumors, delayed puberty and prostate inflammation, and is known to turn male frogs into females, EWG says. In 2000, the Environmental Protection Agency determined that atrazine is not likely to cause cancer in people. However, the agency is currently reviewing the "state of the science" on atrazine and its health and environmental effects "to ensure that the agency’s regulatory decisions continue to protect public health and the environment," the EPA says. Buying organic produce and using a filter for drinking water can reduce exposure to atrazine, EWG says.

Phthalates

These chemicals are used in plastics to make the material more flexible, and in many products as dissolving agents, according to the Centers for Disease Control and Prevention. They can be found in detergents, plastic clothes (raincoats) and even personal care products, such as soaps, shampoos and nail polishes, CDC says. Animal studies suggest that phthalates can affect the reproductive system, but the effect on humans from exposure to low levels of phthalates is unknown, the CDC says. To lower phthalate exposure, people can avoid plastic food containers and plastic wrap made from PVC, EWG says. Personal care products that list "fragrance" as an ingredient may also contain phthalates. EWG says.

Perchlorate

This chemical is used to produce rocket fuel and other explosives, and it can be found in many produce and milk products, EWG says. Too much perchlorate can affect the ability of the thyroid gland to make hormones. Although it is hard to avoid perchlorate in food, people can reduce the effects of the chemical by making sure to consume enough iodine in the diet, EWG says. The EPA is developing regulation that would put a limit on the amount of perchlorate that can be in drinking water. A reverse osmosis filter can also reduce levels of perchlorate in drinking water, EWG says.

Fire retardants

Chemicals used as fire retardants, called polybrominated diphenyl ethers (PBDEs) are very persistent in the environment. They can disrupt thyroid activity, and have been linked to health effects such as lower IQ, according to EWG. Many PBDEs have been phased out, but because of their long-life, they will likely contaminate wildlife for decades, EWG says.

Lead

This is a well-studied toxin, and has been linked to brain damage, lower IQ, hearing loss and nervous system problems, EWG says. But lead has also been found to affect hormones. In animals, lead can lower sex hormone levels, EWG says.

Perfluorinated chemicals (PFCs)

These chemicals are found in no-stick cookware and are very persistent. Some PFCs have been linked to lower sperm quality, low birth weight and thyroid disease, among other problems, EWG says. However, these studies cannot prove PFCs causes these problems, so more research is needed to better determine the effect of PFCs on the human body.

Mercury

This metal is known to interfere with fetal brain development. It can also bind to a hormone that regulates woman's ovulation, and can damage cells in the pancreas that produce the hormone insulin, EWG says. The organization recommends eating wild salmon and trout to reduce mercury exposure. The EPA recommends that women who are pregnant or considering becoming pregnant consume no more than 12 ounces (2 average meals a week) of fish low in mercury (canned light tuna, salmon, pollock, and catfish.)

Arsenic

This element is naturally found in the environment, and also in some pesticides, and so it can find its way into food and drinking water. One form of arsenic, inorganic arsenic, is a known carcinogen, and chronic exposure to low levels of it has been linked to increased risks of bladder, lung and skin cancers. The element may also interfere with the way the body processes sugars and carbohydrates, EWG says. The Food and Drug Administration said recently that levels of arsenic in rice do not appear to pose health risks over the short term, but the agency is still investigating the potential long-term effects.

Organophosphate pesticides

Exposure to these pesticide chemicals has been linked to effects on brain development, behavior and fertility, and can affect testosterone levels, EWG says. Buying organic produce may reduce exposure to these chemicals, EWG says.

Glycol ethers

These chemicals are used as solvents in paints and cleaning products and have been linked to lower sperm count in painters, among other health problems, EWG says. Exposure to these chemicals has also been linked to asthma and allergies in children. Avoiding products with the ingredients 2-butoxyethanol (EGBE) and methoxydiglycol (DEGME) may help reduce exposure to glycol ethers, EWG says.

An environmental health advocacy organization has released a list of what it says are the 12 worst hormone-disrupting chemicals.

These chemicals, known as endocrine disruptors, interfere with the actions of hormones in the human body in some way — for instance, by imitating natural hormones, or increasing or decreasing hormone production, according to Environmental Working Group (EWG), the organization that put together the list.

The list includes some chemicals that have been scrutinized for their potential ability to interfere with hormones and affect reproduction, such as bisphenol A (BPA) and phthalates, although studies on these chemicals are not definitive. [5 Ways to Limit BPA in Your Life]

Other chemicals on the list — such as arsenic, mercury and lead — may surprise consumers, as people may not be aware that these chemicals disrupt hormones, according to EWG.

And still other chemicals might be less familiar to consumers, such as glycol ethers, which are solvents in paints and cleaning products that have been linked to lower sperm count, among other health problems, in painters, according to EWG.

The list also includes: dioxin, atrazine, phthalates, perchlorate, fire retardants, perfluorinated chemicals (PFCs) and organophosphate pesticides. [For the full list, see: 12 Hormone-Disrupting Chemicals & Their Health Effects]

Dr. Kenneth Spaeth, director of the Occupational and Environmental Medicine Center at North Shore University Hospital in Manhasset, N.Y., said the list was reasonable. "The larger value of a list like this is raising the discussion about endocrine-disrupting chemicals," Spaeth said.

While it is generally accepted that there is no safe level of exposure to chemicals like lead, there is still a lot of work to be done in determining whether other chemicals, such as BPA and phthalates, pose a risk to human health at the concentrations present in the environment, Spaeth told LiveScience.

"Endocrine-disrupting chemicals are a work in progress in determining what levels are, indeed, hazardous," Spaeth said. Still, "there's enough evidence for many of these [chemicals] that it's reasonable to have some concern about them," he said.

Spaeth said he might not have included lead, organophosphate pesticides and perchlorate on the list, because use of these chemicals has declined considerably in recent years, significantly lowering people's level of exposure to these chemicals.

The full list, which is intended for readers of all ages, includes ways for consumers to avoid exposure to these chemicals. However, EWG says that ultimately, the best solution is better regulation to prevent such chemicals from coming to the market.

Follow Rachael Rettner @RachaelRettner. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

The endocrine system

The body's hormones, and the glands that produce them, make up the endocrine system. There are eight major glands, and their job is to regulate the body's metabolism, reproduction, growth and sleep.

Like the nervous system, the endocrine system is an information signal system. But rather than using neurons, it uses chemical messengers called hormones, each of which has its own unique function.

Here are 11 interesting facts that may surprise you about the endocrine system, its glands and its hormones.

Traditional Chinese healers practiced endocrinology more than 2,000 years ago.

Endocrinology is the branch of biology and medicine that focuses on the endocrine system, and although the terms "endocrine" and "endocrinology" didn't come into common usage until the 1800s, the study of endocrinology can be traced back to China over 2,000 years ago, according to American author Robert K. G. Temple in his book, "The Genius of China: 3,000 Years of Science, Discovery, and Invention" (Prion, 1998).

As far back as 200 B.C., Chinese healers extracted sex and pituitary hormones from human urine using the sulfate mineral gypsum and the chemical compound saponin (derived from the seeds of a flowering plant). They used these extracts for medicinal purposes.

The endocrine system is sometimes at fault for osteoporosis.

Osteoporosis is a common disease in aging people, and makes bones less dense and more prone to fractures. Nearly one in 10 older adults in the U.S. has the disorder, according to the Centers for Disease Control and Prevention.

Though osteoporosis is often thought of as strictly a bone disorder, it often falls under the treatment of endocrinologists because of its underlying causes. In particular, postmenopausal women sometimes develop the disease because of their low levels of the hormone estrogen, which helps to maintain bone mass. In such cases, osteoporosis may be treated with hormone replacement therapy.

The condition can also arise as a result of other endocrine disorders, such as hyperthyroidism (overactive thyroid). People with such conditions are considered to have "secondary osteoporosis."

The term "hormone" is only about a century old.

In the 1800s, scientists began to think that some sort of chemical communication must take place between different organs in the body, and they later recognized that certain disorders could be treated with extracts from endocrine tissues. But the term "hormone" wasn't coined until the early 1900s.

In 1902, English physiologists William Bayliss and Ernest Starling concluded that chemicals — which they later named hormones — controlled the secretions of the pancreas. This idea ran contrary to the prevailing view that neural reflexes triggered the secretions. (Scientists later discovered that both hormonal and neural processes played a role in pancreatic secretions).

The new term sparked intense research on the endocrine system in the first half of the 20th century, and scientists fervently worked to identify and understand the various hormones in the body.

Not all hormones come from the endocrine system.

The eight hormone-secreting glands of the endocrine system are the adrenal gland, hypothalamus, pancreas, parathyroid gland, pineal gland, pituitary gland, reproductive glands (ovaries and testes) and thyroid gland. But some other organs and tissues that are not generally considered part of the endocrine system also produce and secrete hormones.

For instance, the placenta of a pregnant woman secretes a few hormones, including estrogen and progesterone. And the stomach releases the hunger-inducing hormone ghrelin and the hormone gastrin, which stimulates the secretion of gastric acid.

Diabetes was once diagnosed by tasting urine.

Diabetes — a disease in which the pancreas stops producing insulin, the hormone that regulates blood sugar levels — is the most common endocrine disorder in the U.S., affecting about 8 percent of the population, according to the National Institute of Diabetes and Digestive and Kidney Diseases. Today, physicians use blood tests to diagnose the disease, but a different method was once common. [The Fascinating History of Urine Tests]

The ancient Greek physician Hippocrates (c. 460-377 B.C.), the "Father of Medicine," was the first physician known to diagnose diabetes mellitus, according to a 2000 article in the Journal of General Internal Medicine. His technique: tasting his patients' urine for a distinct sweetness.

The pancreas bridges two worlds.

There are two types of glands in the body: exocrine and endocrine. Exocrine glands — which include the salivary glands, sweat glands and mammary glands — excrete their products through ducts. Endocrine glands, by contrast, release their products (hormones) without ducts, directly into the bloodstream.

The pancreas has both endocrine and exocrine functions. On one hand, it releases a number of hormones, including insulin and glucagon, into the bloodstream. But it also secretes a pancreatic juice that contains important digestive enzymes via ducts into the small intestine.

Alcohol has widespread effects on the endocrine system.

It's well known that alcohol can affect your health in a number of ways, such as decreasing your risk of heart disease and stroke (if consumed in low doses) and damaging your liver. But scientists have known for decades that alcohol also has widespread effects on the endocrine system.

For example, alcohol can impair the regulation of blood-sugar levels by interfering with certain hormones, reduce testosterone levels in men by damaging the testes and increase the risk of osteoporosis by messing with a calcium-regulating hormone called parathyroid hormone, according to the National Institute on Alcohol Abuse and Alcoholism.

Dogs were once an important part of endocrine research.

In the late 19th century and early 20th century, many endocrine-system studies were conducted on dogs, rather than on more typical lab animals, such as mice and guinea pigs.

In 1889, German physiologist Oskar Minkowski and German physician Josef von Mering induced diabetes in dogs by removing their pancreases. Five years later, English physiologist Sir Edward Albert Sharpey-Schafer and English physician George Oliver took extracts from the adrenal glands of dogs and injected them into other dogs, which resulted in hypertension and rapid heartbeat (because of the adrenaline present in the injected substances).

Dogs were even the test subjects in the 1902 landmark study that led to the coining of the term "hormone."

An early endocrinologist attempted hormone replacement therapy on himself.

In 1849, German physiologist and zoologist Arnold Adolph Berthold noticed that roosters' combs regressed and that they lost their inclination to crow, fight and mate if he castrated them. However, reimplanting their testes reversed these effects.

Berthold concluded that the testes excreted a substance that affected the blood; the blood, in turn, acted upon the rest of the body.

Fifty years later, endocrinologist Charles-Édouard Brown-Séquard took this idea to the next level. He injected himself with extracts from dog and guinea-pig testes in a pioneering attempt at a kind of hormone replacement therapy. In the journal The Lancet, the 72-year-old scientist reported that the treatment rejuvenated him, restoring his strength, digestive functions and "intellectual labor."

However, the effects were fleeting, and most experts now view Brown-Séquard's rejuvenation as the result of the placebo effect.

Stress kicks the endocrine system into high gear.

In response to stress, the endocrine system quickly secretes various hormones at higher-than-normal levels in order to help the body mobilize more energy and adapt to new circumstances.

For example, the pituitary-adrenal axis starts releasing adrenaline to increase the volume of blood pumped out by the heart and the blood flowing to the skeletal muscles. And during acute physical stress, the pituitary gland may also ramp up the secretion of the growth hormone, which enhances metabolic activity.

But prolonged or frequent stressful events can lead to a number of endocrine disorders, including Graves' disease, gonadal dysfunction and obesity, according to a 2011 article in the Indian Journal of Endocrinology and Metabolism.

Plants produce hormones without an endocrine system.

Unlike humans and other animals, plants do not have an endocrine system or endocrine glands. But they do have hormones, which affect various processes related to plant growth, including gene expression, metabolism and cell division.

Plant cells sometimes produce hormones to use locally, but they may also transport the chemicals to other areas using specialized elongated cells or other means.

Knowing that plants use hormones to guide their growth, agriculturalists have been using hormonelike chemicals called "plant growth regulators" since the 1930s to improve or otherwise modify the growth of their crops, according to University of Florida agronomist Frederick Fishel.

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A 30-year-old woman in Japan who was thought to be infertile recently gave birth to a healthy baby boy thanks to an experimental fertility treatment, researchers report.

The woman had stopped having regular periods due to a condition called primary ovarian insufficiency, in which the ovaries fail to produce normal amounts of estrogen and do not release eggs regularly.

The researchers removed an ovary, treated it outside the body, and reimplanted it. The treatment stimulated the production of follicles, which are structures that surround developing eggs.

Then, the researchers collected eggs from the woman, fertilized them in a dish with her husband's sperm, and transplanted the embryos into the woman. She gave birth after 37 weeks of pregnancy.

However, the treatment will not work in all women with primary ovarian insufficiency, and currently has a low success rate, the researchers said. [5 Myths About Fertility Treatments]

Only about half of the 27 women in the study (48 percent) were candidates for the treatment, and just five out of 13 women who received the therapy produced viable eggs. Just two became pregnant (one has yet to give birth).

Although more work is needed, the researchers said they hope the technique could help women with primary ovarian insufficiency and other types of early menopause, such as menopause caused by cancer treatment. The researchers, from Stanford University in Palo Alto, Calif. and St. Marianna University School of Medicine in Kawasaki, Japan, speculated that it will be several years before the technique is used outside an experimental setting.

Women are born with all of the eggs they will use in their lifetimes, but the eggs need to mature inside follicles. Typically, one follicle matures each month, and releases an egg.

About 1 percent of women of reproductive age have primary ovarian insufficiency. The cause is often unknown, although it can be due to follicle damage. While women with this condition may spontaneously become pregnant, egg donation is usually the only way for them to have a child, the researchers said.

Previously, the researchers showed that blocking a particular cellular pathway, called the PTEN pathway, stimulated dormant follicles in mice and human ovaries to produce eggs.

in the new study, the researchers employed a technique that has been used in the past to simulate follicles.The technique, called ovarian fragmentation, involves cutting the ovary into pieces.

The researchers found that when ovarian fragmentation was combined with treatment to block the PTEN pathway, the two treatments together activated more follicles than either treatment alone.

After performing these two treatments on the ovary outside the body, small pieces of the ovary are transplanted near the fallopian tubes. Women also need to take drugs to help stimulate the follicles.

One day, it may be possible to get the same results as ovarian fragmentation by blocking a separate pathway, without the need to cut the ovaries, said the researchers, who plan to study this.

The study is published this week in the journal Proceedings of the National Academy of Sciences.

Follow Rachael Rettner @RachaelRettner. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.

When a particular circuit in the brain is stimulated, it causes mice to voraciously gorge on food even though they are well fed, and deactivating this circuit keeps starving mice from eating, a new study shows.

The findings suggest that a breakdown within this neural network could contribute to unhealthy eating behaviors, the researchers said, although more work is needed to see whether the findings are also true of people.

The circuit lies in a brain area called the "bed nucleus of the stria terminalis" (BNST), and affects eating by inhibiting activity in another region, called the lateral hypothalamus, which is known to control eating, according to the study, published today (Sept. 26) in the journal Science.

"Normally, there's a population of neurons in the lateral hypothalamus that's putting the brakes on eating," said study researcher Garret Stuber, a neuroscientist at the University of North Carolina at Chapel Hill. "But when you shut those cells down by stimulating this pathway, that releases the brake, and the animal starts to eat."

The lateral hypothalamus has been known for more than 50 years to be an important part of the brain for controlling eating. Scientists had learned that putting stimulating electrodes in the lateral hypothalamus of animals would influence their eating behavior, but exactly how it works has been a mystery.

"Nobody had a good mechanistic explanation for what's actually being stimulated or activated within this brain structure," Stuber said.

In the new study, the researchers focused on examining how the BNST influences activity in the lateral hypothalamus.

To manipulate the BNST neurons, the researchers used a technique called optogenetics that allowed them to activate specific neurons using light. They found that, upon activation, BNST neurons suppressed activity in the lateral hypothalamus, and caused the well-fed mice to immediately start eating.

"When we stimulate the pathway, the animals eat a third to 50 percent of the calories they eat in a normal day, in about 20 minutes," Stuber said. For a person, that would probably be the equivalent of eating lunch and dinner in one sitting, he said. [7 Foods You Can Overdose On]

What's more, the researchers gave the animals a choice in some of the experiments between regular food and a tasty food with a high fat content, analogous to junk food. They found that when they activated the circuit, the animals showed a strong preference for the junk food.

Conversely, deactivating the circuit caused the animals to immediately stop eating, even if their stomachs were empty.

The BNST is thought to be a hub that integrates emotionally relevant information coming from several parts of the brain. Although the experiments didn't aim to study the link between emotional states and feeding behavior, the findings may explain how emotions can influence eating, Stuber said.

"BNST is really important for affective behavior state in response to emotionally relevant stimuli, and the results show the output of those cells can actually directly modulate feeding behavior," he said.

Identifying a neural circuit that controls feeding, and understanding how the cells in this circuit work, could lead to future treatments for such conditions as obesity, the researchers said.

"Now that we know this is a critical circuit for feeding, we can start looking at this in humans," Stuber said.

Email Bahar Gholipour. Follow LiveScience @livescience, Facebook & Google+. Original article on LiveScience.