Blood Vessels: Tunics, Arteries, Veins, and capillary structure

Arteries

1.) Walls are thicker than veins. 2.)In particular, Tunica media needs to be much thicker and heavier and contain substantially more smooth muscle and elastic tissue. 3.) closer to the pumping action of the heart 4.) must be able to expand as an increased volume of blood is propelled into them during systole, and recoil during diastole.

Capillaries

1.) contain only a tunica intima 2.) provide the exchange of materials (gases, nutrients, etc.) between blood and tissue cells.

arterioles

1.) smallest arteries w/ a very thin tunica external and only a few layers of of smooth muscle in the tunica media. 2.) Blood flows form arterioles into a capillary bed. They play a role in regulating the blood flow to specific areas of the body.

Veins

1.) valves act to prevent back flow of blood in much the same manner as the semilunar valves of the heart. 2.) the skeletal muscle "pump" promotes the venous return; as the skeletal muscles surrounding the veins contract and relax. 3.) contain more fibrous tissue in the tunica externa than the corresponding arteries. 4.) larger lumen than corresponding arteries.

Tunica Intima

Lines the lumen of a blood vessel and is composed of a single layer of endothelium , subendothelial layer, and an internal elastic membrane. Cells fit closely together to form an extremely smooth blood vessel lining that helps decrease blood flow resistance.

Tunica Media

middle coat that is composed primarily of smooth muscle and elastin. The smooth muscle plays an active role in regulating the diameter of blood vessels, which in turn alters peripheral resistance and blood pressure.

Tunica externa

outermost tunic composed of areolar or fibrous connective tissue. Its function is basically supportive and protective. In larger vessels it contains a system of blood vessels called the Vasa Vasorum.