What are Kidneys?

Your kidneys are a pair of vital organs that perform many functions to keep your blood clean and chemically balanced.

Your kidneys are bean-shaped organs, each about the size of a fist.

Your kidneys are located near the middle of your back, just below your rib cage, one on each side of your spine.

Your kidneys are sophisticated reprocessing machines. Every day, your kidneys process about 200 quarts of blood to sift out about 2 quarts of waste products and extra water. The wastes and extra water become urine, which flows to your bladder through tubes called ureters. The bladder stores urine until releasing it through urination.

The actual removal of wastes occurs in tiny units inside the kidneys called nephrons. Each kidney has about a million nephrons. In the nephron, a glomerulus – which is a tiny blood vessel, or capillary – intertwines with a tiny urine-collecting tube called a tubule. The glomerulus acts as a filtering unit, or sieve, and keeps normal proteins and cells in the bloodstream, allowing extra fluid and wastes to pass through. A complicated chemical exchange takes place, as waste materials and water leave the blood and enter the urinary system.

Hormones

Your kidneys also release three important hormones:

• Erythropoietin (EPO) – stimulates the bone marrow to make red blood cells.
• Renin – regulates blood pressure.
• Calcitriol – the active form of vitamin D, which helps maintain calcium for bones and for normal chemical balance in the body.

Source: kidney.niddk.nih.gov – February 2009