RLO: The Anatomy of the Kidneys


Internal Structure

Viewed internally, the kidney has an outer layer of outer cortex which surrounds the inner medulla.

The medulla consists of a number of medullary pyramids, named because of their triangular shape. These are striped in appearance because they contain microscopic coiled tubes called nephrons, the functional unit of the kidney .

Urine is made by the nephrons and drains into tiny collecting ducts within the medullary pyramids. The collecting ducts merge at the base of the pyramids to form the renal papilla.

From the papilla, urine drains into cuplike structures called the major and minor calyces. From the calyces the urine drains into the wider open space of the renal pelvis. This acts like a funnel draining the urine out of the kidney into the ureter.