The inner portion of the kidney, known as the middle layer, is called the

• A. Cortex
• B. Pelvis
• C. Calyx
• D. Medulla

Answer: (D)

This item tests kidney anatomy and its regional organization. The outer layer is the cortex, while the inner portion—the tissue that lies beneath the cortex—is the medulla. The medulla contains the renal pyramids and houses the loops of Henle and the collecting ducts, which are essential for concentrating urine. The calyces and the renal pelvis are parts of the drainage/collecting system that channel urine from the medulla outward, but they are not the inner tissue layer itself. Therefore, the inner portion is the medulla.