Structure of the Vein Wall
The vein wall consists of three layers:
- Tunica Adventitia - the strong outer covering of arteries and veins. It is composed of connective tissue as well as collagen and elastic fibers. These fibers allow the arteries and veins to stretch to prevent overexpansion due to the pressure that is exerted on the walls by blood flow.
- Tunica Media - the middle layer of the walls of arteries and veins. It is composed of smooth muscle and elastic fibers. This layer is thicker in arteries than in veins.
- Tunica Intima - the inner layer of arteries and veins. In arteries this layer is composed of an elastic membrane lining and smooth endothelium (special type of epithelial tissue) that is covered by elastic tissues. Veins do not contain the elastic membrane lining that is found in arteries. In some veins the tunica intima layer also contains valves to keep blood flowing in a single direction.