Gross specimen of a cross-section through a healthy kidney. The kidneys filter waste from the blood and excrete it as urine. Each kidney consists of an outer paler cortex and an inner darker medulla. The medulla is divided into regions called renal pyramids. Each renal pyramid drains into a renal papilla (white). The renal papillae merge to form the ureter (not seen), which carries the urine to the bladder.