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