Blood vessels. Scanning electron micrograph (SEM) of a resin cast of pancreatic blood vessels. The fine network of smaller vessels that branches off from the main vessels 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 pancreas produces the hormones insulin and glucagon, which regulate blood glucose levels. It also secretes digestive enzymes. The cast was made by injecting resin into the blood vessels, followed by chemical digestion of surrounding tissues. Magnification: x30 at 6x7cm size.