In the human body, the kidneys are located vertically in the middle of the abdomen near the back wall. They are beneath the rib cage with one kidney on either side of the spine. Other mammals also have kidneys in the rear abdominal area.
Kidneys filter waste out of the bloodstream and maintain the body's level of water and minerals. Their location gives them easy access to the bloodstream through the renal artery. After the blood is filtered, it returns to the body through the renal vein. Wastes removed from the bloodstream leave the body as urine, which moves from the kidney through the ureters into the bladder and then out of the body through the urethra. Each kidney is about 2 inches wide and 5 inches long.