Each kidney has a concave medial border, the hilum—where nerves enter, the ureter exits, and blood and lymph vessels enter and exit—and a convex lateral surface, both covered by a thin fibrous capsule (Figure 1). The expanded upper end of the ureter, called the renal pelvis, divides into two or three major calyces. Smaller branches, the minor calyces, arise from each major calyx. The area surrounding the calyces, called the renal sinus, usually contains considerable adipose tissue.
Each kidney is bean-shaped, with a concave hilum where the ureter and the renal artery and veins enter. The ureter divides and subdivides into several major and minor calyces, around which is located the renal sinus containing adipose tissue. Division of the parenchyma into cortex and medulla can also be seen grossly. Attached to each minor calyx is a renal pyramid, a conical region of medulla delimited by extensions of cortex. A renal pyramid with associated cortex constitutes a renal lobe. The cortex and hilum are covered with a fibrous capsule.
The kidney has an outer cortex and an inner medulla (Figures 1 and 2). In humans, the renal medulla consists of 8–15 conical structures called renal pyramids, which are separated by cortical extensions called renal columns. Each medullary pyramid plus the cortical tissue at its base and along its sides constitutesa renal lobe (Figure 1).