Stock Photo - KIDNEY, DRAWING<BR>The kidney belongs to the urinary system. It is the organ that produces the urine. It has the shape of a bean and is around 12 cm long. It is embedded in a fibrous capsule containing the renal functional tissue ( parenchyma ). The parenchyma is constituted of the cortex and medulla. This tissue produces the urine thanks to nephrons ( shapes of a glomerulus and a renal tube ). The main function of the kidney is to eliminate the wastes and maintain the acid-base equilibrium of the blood. But it also secrete an hormone ( playing a role in the maturation red corpuscles ) and a enzyme ( that regulates the blood pressure ).