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Endocrine System: Facts, Functions and Diseases

abdomen, pancreas, anatomy
The pancreas is located deep inside the abdomen.
Credit: Sebastian Kaulitzki

The endocrine system is the collection of glands that produce hormones that regulate metabolism, growth and development, tissue function, sexual function, reproduction, sleep, and mood, among other things.

The endocrine system is made up of the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, pancreas, ovaries (in females) and testicles (in males), the Mayo Clinic notes.  

The word endocrine derives from the Greek words "endo," meaning within, and "crinis," meaning to secrete, according to Health Mentor Online. In general, a gland selects and removes materials from the blood, processes them and secretes the finished chemical product for use somewhere in the body. The endocrine system affects almost every organ and cell in the body, according to the Merck Manual.

Although the hormones circulate throughout the body, each type of hormone is targeted toward certain organs and tissues, the Merck Manual notes. The endocrine system gets some help from organs such as the kidney, liver, heart and gonads, which have secondary endocrine functions. The kidney, for example, secretes hormones such as erythropoietin and renin.

Diseases of the endocrine system

Hormone levels that are too high or too low indicate a problem with the endocrine system. Hormone diseases also occur if your body does not respond to hormones in the appropriate ways. Stress, infection, and changes in the blood's fluid and electrolyte balance can also influence hormone levels, according to the National Institutes of Health.

The most common endocrine disease in the United States is diabetes, a condition in which the body does not properly process glucose, a simple sugar. This is due to the lack of insulin or, if the body is producing insulin, because the body is not working effectively, according to Dr. Jennifer Loh, chief of the department of endocrinology for Kaiser Permanente in Hawaii.

Hormone imbalances can have a significant impact on the reproductive system, particularly in women, Loh explained.  

Another disorder, hypothyroidism, occurs when the thyroid gland does not produce enough thyroid hormone to meet the body’s needs. Loh noted that insufficient thyroid hormone can cause many of the body's functions to slow or shut down completely.

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, according to Loh.

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. While Loh noted that the condition can occur in people not undergoing treatment for diabetes, such an occurrence is fairly rare.

Causes and treatment of endocrine diseases

Diabetes, the most common disease of the endocrine system, can be linked to obesity, diet and family history, according to Dr. Alyson Myers of North Shore-LIJ Health System. "To diagnose diabetes, we do an oral glucose tolerance test with fasting."

It is also important to understand the patient's health history as well as the family history, Myers noted.

Tumors — both benign and cancerous — can also disrupt the functions of the endocrine system, Myers explained. Infections and medications such as blood thinners can also cause adrenal deficiencies.

Diabetes is treated with pills or insulin injections. Managing other endocrine disorders typically involves stabilizing hormone levels with medication or, if a tumor is causing an overproduction of a hormone, by removing the tumor. Treating endocrine disorders takes a very careful and personalized approach, Myers said, as adjusting the levels of one hormone can impact the balance of other hormones.

What is an endocrinologist?

After completing four years of medical school, people who want to be endocrinologists then spend three or four years in an internship and residency program. These specialty programs cover internal medicine, pediatrics, or obstetrics and gynecology, according to the American Board of Internal Medicine.

Endocrinologists-in-training then spend two or three more years learning how to diagnose and treat hormone conditions. Overall, an endocrinologist's training will take more than 10 years after the undergraduate degree. They are certified by the American Board of Internal Medicine. Endocrinologists typically specialize in one or two areas of endocrinology, such as diabetes or infertility. These specialists treat patients with fertility issues and also assess and treat patients with health concerns surrounding menstruation and menopause, Loh noted.

endocrine system
The Endocrine System
Credit: Alila Sao Mai | Shutterstock

Milestones in the study of the endocrine system

200 B.C.: The Chinese begin isolating sex and pituitary hormones from human urine and using them for medicinal purposes

1025: In medieval Persia, the writer Avicenna (980-1037) provides a detailed account on diabetes mellitus in "The Canon of Medicine" (c. 1025), describing the abnormal appetite, the collapse of sexual functions and the sweet taste of diabetic urine.

1835: Irish doctor Robert James Graves describes a case of goiter with bulging eyes (exophthalmos). The thyroid condition "Graves' disease" was later named after the doctor.

1902: William Bayliss and Ernest Starling perform an experiment in which they observe that acid instilled into the duodenum (part of the small intestine) causes the pancreas to begin secretion, even after they had removed all nervous connections between the two organs.

1889: Joseph von Mering and Oskar Minkowski observe that surgically removing the pancreas results in an increase of blood sugar, followed by a coma and eventual death.

1921: Otto Loewi in 1921 discovers neurohormones by incubating a frog's heart in a saline bath.

1922: Leonard Thompson, at age 14, is the first person with diabetes to receive insulin. Drugmaker Eli Lilly soon starts mass production of insulin.

Related:

Facts, Functions & Diseases:

Additional resources

  • Learn about endocrine diseases from the National Institutes of Health.
  • The Merck Manual provides comprehensive information about the endocrine system.
  • The American Association

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Kim Ann Zimmermann

Kim Ann Zimmermann is a contributor to Live Science. She holds a bachelor’s degree in communications from Glassboro State College.
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