Caption

Kidney. Illustration of a section through a whole healthy human kidney. At centre left is the renal artery (red) and vein (blue) which supply blood to, and drain blood from the kidney. The kidney is divided into an outer cortex (brown) and pyramid- shaped units (red) of the inner medulla. Blood is passed into a network of capillaries in the cortex ending in small tight knots called glomeruli (not seen). Glomeruli are blood filtering units from which excess water and metabolic wastes pass from the blood into tubules, where the waste turns to urine. The urine then drains through the medullary pyramids into the ureter (yellow) which passes the urine down into the urinary bladder.