What Are The Types Of Veins?

A vein is a vessel structure that exists throughout the body that transports blood from all parts of the body to the heart. Arterial blood moves through a high-pressure mechanism away from the heart, and the venous blood moves through a low-pressure mechanism and muscle contractions back to the heart. Vein diameter ranges from one millimeter to one and a half centimeters. Veins contain three tissue layers in their walls. Connective tissue, elastic fibers, and collagen fibers make up the tunica adventitia or strong outer layer of the veins and arteries. Elastic fibers and smooth muscle form the tunica media or middle layer of veins and arteries. Smooth endothelium, elastic tissues, and an elastic membrane lining form the tunica intima or innermost layer of veins and arteries. Veins contain muscular structures in the tunica intima that move blood against gravity back to the heart. Veins are classified according to their location and size.