The kidneys, a part of the urinary system, are a pair of bean shaped organs in the back of abdomen. They clean the body of excess water, salt and waste products. As blood circulates through the kidneys, it passes through more than a million tiny filtering units within them. These filters produce a liquid waste, urine.

Urine flows from the kidneys through a pair of thin tubes, the ureters, to the bladder, where it is stored until a person urinates. During urination, the urine leaves the body by passing from the bladder through another tube, the urethra, which is open at one end.

The kidneys also produce important hormones that help regulate blood pressure, form bone, and control red blood cell production in bones.