Kidney anatomy, illustration. The kidneys filter waste from the blood and excrete it as urine. The kidney consists of an outer cortex (red) and an inner medulla. The medulla is divided into regions called the renal pyramids (raised). Each renal pyramid drains into a renal papilla (cream tubes). The renal papillae merge to form the ureter (tube, bottom left), which carries the urine to the bladder. Blood is carried to the kidney by the renal artery (red) and away from it by the renal vein (blue).