Photo de stock - KIDNEY, DRAWING<BR>The kidneys are bean-shaped organs which in humans are approximately 12cm in length. An integral part of the urinary system, the kidneys are the organs which produce the waste product known as urine. They are covered by a fibrous capsule containing the functional tissue, or parenchyma, made up of the renal cortex and medulla. The urine-producing bodies of the kidneys, or nephrons, present in this tissue are each composed of a glomerulus and a renal tubule. The main function of the kidneys is the elimination of waste and the regulation of the blood´s pH balance. They also secrete a hormone which plays a role in the maturation of red blood cells and an enzyme which regulates blood pressure.