Blood vessels. Coloured scanning electron micrograph (SEM) of a resin cast of blood vessels in connective tissue. This network of vessels infiltrates the tissue, supplying it with blood. Gases and nutrients are exchanged between the blood and surrounding tissue through the permeable walls of capillaries, the smallest blood vessels. Connective tissues provide structural support and cohesion throughout the body. This connective tissue supports the thyroid gland of the neck. The cast was made by injecting resin into the blood vessels. The surrounding tissues were then chemically digested. Magnification: x110 at 6x7cm size.