Patients

The kidneys are two bean-shaped organs that filter the blood and the kidneys are part of the urinary system. They remove waste and balance the body’s fluids.

Functions of a kidney

You have two kidneys, each about the size of an adult fist, located on either side of the spine just below the rib cage. Although they are small, your kidneys perform many complex and vital functions that keep the rest of the body in balance. For example, kidneys:

• Production of urine: helps remove waste and excess fluid
• Production of hormones; antidiuretic hormones that control fluid balance
• Filter the blood, keeping some compounds while removing others
• Control the production of red blood cells
• Make vitamins that control growth
• Release hormones that help regulate blood pressure
• Production of erythropoietin and calcitrol
• Help regulate blood pressure, red blood cells, and the amount of certain nutrients in the body, such as calcium and potassium.

Here's how kidneys perform their important work

• Blood enters the kidneys through an artery from the heart
• Blood is cleaned by passing through millions of tiny blood filters
• Waste material passes through the ureter and is stored in the bladder as urine
• Newly cleaned blood returns to the bloodstream by way of veins
• Bladder becomes full and urine passes out of the body through the urethra.

The kidneys perform their life-sustaining job of filtering and returning to the bloodstream about 200 quarts of fluid every 24 hours. Approximately two quarts are eliminated from the body in the form of urine, while the remainder, about 198 quarts, is retained in the body. The urine we excrete has been stored in the bladder for approximately one to eight hours.

© 2015 National Kidney Foundation. All rights reserved. This material does not constitute medical advice. It is intended for informational purposes only. Please consult a physician for specific treatment recommendations.