Final answer:
The middle portion of the kidneys is the renal medulla. It contains the renal pyramids, separated by renal columns, and ends at the renal papillae which drain into the renal pelvis.
Step-by-step explanation:
The middle portion of the kidneys is known as the renal medulla. The renal medulla is situated between the outer region, which is the renal cortex, and the innermost region, the renal pelvis. The medulla is composed of several conical masses called renal pyramids, which are separated by renal columns. The pyramids contain the collecting ducts that transport urine to the calyces of the kidney for excretion. The renal papillae, or the tips of the renal pyramids, point toward the renal pelvis which collects the urine and channels it to the ureter, ultimately draining into the urinary bladder.
Moreover, the renal hilum is the area where the renal artery, vein, ureters, and nerves enter and exit the kidney. The renal pelvis, which branches into major and minor calyces, emerges from the hilum, and the smooth muscle in the pelvis propels urine into the ureter.