urinary system

The human urinary system. At the bottom, the complete system in outline; on the left, the arrangement of blood vessels connected to the kidney; at the top right, a detail of the network of vessels within a kidney.

System of organs that removes nitrogenous waste products and excess water from the bodies of animals. In vertebrates, it consists of a pair of kidneys, which produce urine; ureters, which drain the kidneys; and (in bony fishes, amphibians, some reptiles, and mammals) a bladder that stores the urine before its discharge. In mammals, the urine is expelled through the urethra; in other vertebrates, the urine drains into a common excretory chamber called a cloaca, and the urine is not discharged separately.