Kidney. Computer artwork of of a section through a whole healthy human kidney. The kidney is divided into an outer cortex (orange) and the 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 (orange, at bottom right) which leads to the bladder.