Body of Evidence: The Urinary System

The kidneys rid the body of the waste products of protein metabolism in the form of urea and maintain a balance of salts, water, and other substances. The kidneys unusual approach for ridding the bloodstream of unwanted substances is to essentially throw nearly everything out and then absorb back what the body needs. The three basic functions of the kidneysfiltration, excretion, and absorptionare carried out by nearly 2 million filtering units called nephrons.