Internal structure of kindey
The renal cortex is approximately 5 mm thick. Extensions of the renal cortex project internally and are called renal columns.
The renal columns divide the renal medulla into triangular-shaped tissue collections called the pyramids. Each kidney has more or less 10 to 16 pyramids. The pyramids contain nephrons, which are the functional units of the kidneys.
The bases of the renal pyramids are directed toward the renal cortex (outward). In contrast, the apex of each pyramid projects inward toward the renal sinus, which is a cavity within the kidney. It contains the hilum, renal pelvis, renal calyces, fat tissue, blood vessels, and nerves.
The minor calyces represent the proximal parts of the tubes that will eventually form the two ureters. They receive urine from the papillary ducts. Several minor calyces fuse and form a major calyx. Two or three major calyces combine to form the renal pelvis, a funnel-shaped superior end of each ureter.