Diagram of a nephron, the functional unit of excretion in the human kidney. Blood circulating in branches of the renal artery (red) is filtered through a knot of capillaries (the glomerulus, red knot) into the surrounding Bowman's capsule (green, cup-shaped). Water, nitrogenous waste & other substances pass into the proximal renal tubule (green) where most substances are re- absorbed back into the blood. The remaining fluid, now termed urine, passes through the distal convoluted tubule (bending, yellow section) and into the collecting duct (right) which drains into the ureter & eventually reaches the urinary bladder.