Blood Vessel Structure

Blood Vessel Layers Three (3) main layers - endothelium, smooth muscle, and connective tissue

Blood Vessels Five (5) different types of blood vessels

Summary of five types of blood vessels There are five main types of blood vessels: arteries, arterioles, capillaries, venules and veins. Arteries carry blood under pressure away from the heart to other parts of the body. Arteries leave the heart and divide into small arteries called arterioles. Arterioles play in an important role in controlling blood pressure. When arterioles enter a tissue, they branch into numerous tiny vessels called capillaries. Capillaries have a thin cell wall and allow the exchange of substances between the blood and body tissues. Groups of capillaries within a tissue reunite to form small veins called venules. Venules in turn merge to form progressively larger blood vessels called veins. Veins are the blood vessels that convey blood from tissues back to the heart.

Artery Structure Arteries The wall of an artery has the three layers of a typical blood vessel, but has a thicker muscular-to-elastic tunica media. Due to their plentiful elastic fibers their walls stretch easily or expand without tearing in response to an increase in pressure (beating heart)

Arterioles Arterioles have a thin tunica interna with a thin, fenestrated internal elastic lamina They consist of one to two layers of smooth muscle cells having a circular orientation in the vessel wall. The terminal end of the arteriole, the region called the metarteriole, tapers toward the capillary junction. They contain precapillary sphincters which monitor the blood flow into the capillaries, the other muscle cells in the arteriole regulate the resistance to blood flow. Arterioles have a big influence on regulating blood pressure

Capillaries Capillaries , the smallest of blood vessels, that connect the arterial outflow to the venous return. Capillaries form an extensive network, approximately 20 billion in number, of short, branched, interconnecting vessels that course among the individual cells of the body. This network forms an enormous surface area to make contact with body's cells. The primary function of capillaries is the exchange of substances between the blood and interstitial fluid. Because of this, these thin-walled vessels are referred to as exchange vessels.

Venules Unlike their thick-walled arterial counteparts, venules and veins have thin walls that do not readily maintain their shape. Venules drain the capillary blood and begin the return flow of blood back toward the heart. Venules join together to form veins carrying blood back to the heart

Vein Structure Veins, in general, have very thin walls relative to their total diameter (large lumen). They range in size from 0.5 mm in diameter for small veins to 3 cm in the large caval veins entering the heart. Veins have one-way valves that prevent back flow of blood. Blood under low (0) pressure is squeezed by skeletal muscles back to the heart.