The kidneys are two bean shaped organs, each about the size of your fist. They are located in the middle of the back on either side of the spine and receive about 20 % of the blood pumped by the heart. The kidneys play a very important role in the body. They are responsible for regulating the content of the blood by controlling water volume and removing waste. They also regulate blood pressure, maintain calcium balance in the body and play a role in the production of red blood cells.