Illustration of a section through the left kidney. The kidneys filter waste products from the blood and excrete them as urine. Each kidney consists of an outer cortex and an inner medulla. The medulla is divided into regions called the renal pyramids (striped). Each renal pyramid drains into a renal papilla (smaller white tubes). The renal papillae merge to form the ureter (large white tube emerging from kidney), which carries the urine to the bladder. Blood is carried to the kidneys by the renal arteries (turquoise) and away from them by the renal veins (not shown). From 'Traite d'Anatomie Humaine', Vol. 4 (1905) by French anatomist Leo Testut (1849-1925).