The kidneys are two bean-shaped organs, each about the size of a fist. They are located just below the rib cage, one on each side of the spine. Every day, the two kidneys filter about 120 to 150 quarts of blood to produce about 1 to 2 quarts of urine, composed of wastes and extra fluid. The urine flows from the kidneys to the bladder through two thin tubes of muscle called ureters, one on each side of the bladder. The bladder stores urine. The muscles of the bladder wall remain relaxed while the bladder fills with urine. As the bladder fills to capacity, signals sent to the brain tell a person to find a toilet soon. When the bladder empties, urine flows out of the body through a tube called the urethra, located at the bottom of the bladder. In men the urethra is long, while in women it is short.

Another word for kidney is renal. You may hear your doctor talk about renal function or read materials that mention renal failure. Whenever you see or hear the word renal, you will know the subject is about kidneys.

They kidneys have a couple of different functions. Their main purpose of the kidney is to separate urea, mineral salts, toxins, and other waste products from the blood, especially a nitrogen-containing compound called urea.