Which of the following is NOT an internal region of the kidney?

The hilum of the kidney is not classified as an internal region. Instead, it is the area where blood vessels, lymphatics, nerves, and the ureter enter and exit the kidney. This anatomical feature serves as a crucial passageway for these structures, making it important for kidney function but distinct from the internal regions.

In contrast, the pelvis, cortex, and medulla are all integral components of the kidney's internal structure. The cortex is the outer layer, containing glomeruli and convoluted tubules, while the medulla consists of renal pyramids and the collecting ducts, playing key roles in urine formation and concentration. Understanding these parts is essential for comprehending kidney function and pathology more thoroughly.