Veins, Venules, Venous Valves + Blood Reservoirs

Veins

Outnumber arteries; Thin walls, fewer elastic fibers, and less smooth muscle; Large lumens can hold up to 70% of the total blood volume making veins Blood Reservoirs

Venules

Smallest veins; Drain blood from capillary beds

Postcapillary Venules

Have endothelium with some connective tissue and allow exchange

Larger Venules

As venules merge to become larger venules, the three tunics become more distinct

Venous Valves

Extensions of the tunica intima; Prevent backflow in the veins; Numerous in the legs

Elastic Arteries Structure

Large arteries with well-developed elastic laminae

Elastic Arteries Function

Conduct blood under high pressure to organs

Muscular Arteries Structure

Thick-walled arteries with a well-developed tunica media

Muscular Arteries Function

Control blood flow to organs; Regulate blood pressure

Arterioles Structure and Function

Thin walls with all three tunics; Control blood flow to tissues; Feed capillary beds

Venules Structure and Function

Small venules have only a tunica intima; larger venules have all three tunics; Drain capillary beds

Veins Structure and Function

Thin-walled vessels with a large lumen, little smooth muscle, and valves; Return blood to the heart