The nephron is the functional unit of the kidney, the structure that actually produces urine by removing waste and excess substances from the blood. The renal cortex is the outer portion of the kidney between the renal capsule and the renal medulla. The renal medulla is the innermost part of the kidney. The renal medulla is split up into a number of sections, known as the renal pyramids. The renal pelvis is the funnel-like dilated proximal part of the ureter in the kidney. The ureter is the tube that carries urine from the kidney to the urinary bladder. In humans, there are two ureters, one attached to each kidney. Thus, the correct answer is option D.