Hepatic blood vessels. Coloured scanning electron micrograph (SEM) of a resin cast of blood vessels in the liver. The fine network of smaller vessels that branches off from the main vessel infiltrates the tissue, supplying it with blood. Gases and nutrients are exchanged between the blood and surrounding tissues through the permeable walls of capillaries, the smallest blood vessels. The liver produces many important biochemicals, as well as regulating sugar and fat levels in the blood, and clearing the blood of toxins. The cast was made by injecting resin into the blood vessels, followed by chemical digestion of surrounding tissues. Magnification: x70 at 6x7cm size.