Kidneys are the organs that are responsible for filtering the blood and balancing fluids in the body. Aside from its basic functions, it also reacts to hormones that are sent by the brain. Kidneys can even make their own hormones, which include the hormone that tells the body to make red blood cells. Furthermore, filtering the wastes out of the blood is one of the main functions of the kidneys. About 400 gallons of recycled blood are pumped through the kidneys everyday. – words.dictionary.net
