The Kidneys

The urinary system consists of paired kidneys and ureters and a single urinary bladder and urethra. Each kidneys has a cortex (subdivided into outer cortex and juxtamedullary cortex) and a medulla (subdivided into outer medulla and inner medulla).

The medulla is formed by conical masses, the renal medullary pyramids, with their bases located at the corticomedullary junction. A renal medullary pyramid, together with the associated covering cortical region, constitutes a renal lobe. The base of the renal lobe is the renal capsule. The lateral boundaries of each renal lobe are the renal columns (of Bertin), residual structures representing the fusion of primitive lobes within the metanephric blastema. The apex of each renal lobe terminates in a conic-shaped papilla surfaced by the area cribrosa (perforated area; the opening site of the papillary ducts). The papilla is surrounded by a minor calyx. Each minor calyx collects the urine from a papilla dripping from the area cribrosa. Minor calyces converge to form the major calyces which, in turn, form the pelvis.