Illustration of the anatomy of a kidney (left) and the structure of a nephron (right), the functional filtering unit of a kidney. The kidneys filter waste from the blood and excrete it as urine. The filtration occurs in the renal corpuscle where a glomerulus (red capillary bundle, upper centre) is encased in a Bowman's capsule. Waste products drain through the proximal convoluted tubule (folded tube, left), the loop of Henle (thinner part of tube, where water is reabsorbed), and the distal convoluted tubule (folded tube, right), into a collection duct (down right). The nephrons span the kidney's outer cortex and inner medulla. The medulla is divided into regions called the renal pyramids (brown). Each renal pyramid drains into tube, 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).