The kidneys are the main organs of the urinary system. They are bean shaped organs, each about the size of a fist that serve several essential regulatory roles in vertebrates. They are located just below the rib cage, one on each side of the spine. Every day, the two kidneys filter about 120 to 150 quarts of blood to produce about 1 to 2 quarts of urine, composed of wastes and extra fluid.