Concept 1 Review: Structure and Function of Arteries, Capillaries, and Veins
The walls of arteries and veins have three layers or tunics:
• An outer layer (tunica adventitia) of connective tissue with collagen fibers.

• A middle layer (tunica media) of circularly arranged smooth muscle and elastic fibers.

• An inner layer (tunica intima), consisting of a specialized simple squamous epithelium, often called the endothelium, that lines all blood vessels and the endocardium of the heart. The basement membrane, a subendothelial layer composed of connective tissue, supports the endothelium.

Roll your mouse over each of the three types of blood vessels in the graphic to review their structure and function. Be patient, and allow your browser some time to access the new image.
Valves and Blood Return to the Heart
vein artery capillaries