Kidneys: Facts, Function & Diseases

Kidneys are bean-shaped organs located on both sides of the spine, behind the stomach. (Image credit: Lightspring | Shutterstock)

Most people have two kidneys. They are bean-shaped organs located on both sides of the spine, behind the stomach. Each one is about the size of an adult fist. Their main purpose is to keep the composition of blood in the body balanced to maintain good health. 


The kidneys filter extra water and toxins from the blood. The kidneys filter about 120 to 152 quarts (113 to 144 liters) of blood to create 1 to 2 quarts (0.94 to 1.8 l) of urine every day, according to the National Institutes of Health (NIH). 

They aren’t just one big filtering sponge, though. Each kidney is a system of millions of tiny filters called nephrons. A nephron has two parts. The glomerulus is the first part of the filter. It strains blood cells and large molecules from the toxins and fluid. The fluids and toxins that pass through then go through the tubule. The tubule collects minerals that the body needs and puts them back into the bloodstream and filters out more toxins. 

While filtering, the kidneys produce urine to carry the toxins away. The urine is sent through two tubes called ureters down to the bladder, where the urine then leaves the body through the urethra.  

The kidneys also make hormones. These hormones help regulate blood pressure, make red blood cells and promote bone health. 


Poor kidney care and genetics can cause a wide range of health problems. Chronic kidney disease, also called chronic kidney failure, is when the kidneys slowly stop functioning. One in three American adults are at high risk for developing kidney disease, according to the National Kidney Foundation. There are many conditions that can cause kidney disease, including type 1 and 2 diabetes, high blood pressure, obstructions in the urinary tract and inflammation of various parts of the kidneys, according to the Mayo Clinic.

Kidney failure is the most severe stage of kidney disease. It occurs when kidneys stop functioning without help. People with kidney failure need dialysis or a kidney transplant to survive. People with healthy kidneys can donate part of a kidney or a whole kidney to those in need without becoming sick, in most cases. Kidney transplants are one of the most common surgeries in the United States, according to the U.S. National Library of Medicine.

Kidney cancer is the seventh most common type of cancer. According to the Mayo Clinic, the most common type of kidney cancer is renal cell carcinoma. In the United States, 61,560 adults will be diagnosed with kidney cancer and renal pelvic cancer in 2015, and it will be the cause of around 14,080 deaths in 2015, according to the American Society of Clinical Oncology.

Kidney stones are exactly what they sound like. They are stones made from hardened minerals and acid salts that collect in the kidneys, usually formed by concentrated urine. The minerals in the urine crystalize and stick together, according to the Mayo Clinic. Though they are very painful, they usually don’t cause any damage to the body.

Kidney infections, also called pyelonephritis, are usually caused by bacteria that enter the urethra, ascend into the bladder and make their way to the kidneys, according to the Urology Care Foundation. If a kidney infection goes untreated, it can cause permanent kidney damage. 

Promoting good kidney health

Proper care can keep kidneys running properly well into old age. One of the most important things to remember is to stay hydrated. Kidneys need water to function properly and to carry away toxins. 

“In the most serious cases, dehydration can eventually harm the body causing seizures, kidney failure and even death,” said Dr. Buck Parker, a trauma surgeon who also recently appeared on NBC’s reality TV show “The Island.” Parker suggested that the best ways to avoid dehydration included drinking water before you get thirsty, since thirst indicates dehydration; eating foods, like fruits and vegetables, with a high water content; avoiding soda or other caffeinated drinks; and limiting alcohol consumption.

Vitamins can be very important to the function and health of kidneys. “(Folic acid) helps to reduce levels of homocysteine, which has been linked to heart disease, stroke and kidney disease,” said Dr. Kristine Arthur, an internist at Orange Coast Memorial Medical Center in Fountain Valley, California. Vitamin A is also very important to healthy kidney function. 

Taking too much vitamin C, though, may lead to kidney stones, according to Arthur.

Another supplement that may cause trouble is calcium. “Some older women who get their calcium from supplements rather than in their diet are more prone to kidney stones,” said Dr. Linda Girgis, a family practice doctor in South River, New Jersey. “Many people falsely assume that taking vitamins is healthy and safe, but this is not always the case. Sometimes people take too much. It is very hard to get too much when ingesting it is food,” said Girgis. 

Keeping blood pressure in check may also contribute to long-term good kidney health. A study by the National Kidney Foundation found that moderately high blood pressure levels in midlife might contribute to late-life kidney disease and kidney failure.

The American Kidney Fund also suggests avoiding a diet high in fat and salt, limiting alcohol, avoiding tobacco and exercising most days as good ways to keep kidneys healthy. 

Additional resources

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

Parts of the human body

Systems of the human body

Alina Bradford
Live Science Contributor
Alina Bradford is a contributing writer for Live Science. Over the past 16 years, Alina has covered everything from Ebola to androids while writing health, science and tech articles for major publications. She has multiple health, safety and lifesaving certifications from Oklahoma State University. Alina's goal in life is to try as many experiences as possible. To date, she has been a volunteer firefighter, a dispatcher, substitute teacher, artist, janitor, children's book author, pizza maker, event coordinator and much more.