Renal Medulla

The substance of the kidney is divided into two distinct regions: an inner medulla and an outer cortex. The "renal medulla" is composed of conical masses of tissue called "renal pyramids," whose bases are directed toward the convex surface of the kidney, and which apex to form the renal papillae. The "renal cortex" forms a shell around the medulla. Its tissues dip into the medulla between adjacent renal pyramids to form "renal columns." The granular appearance of the cortex is due to the random arrangement of tiny tubules associated with "nephrons," the functional units of the kidney.