Arterioles and Venules
Arterioles are a type of blood vessel that branches off from arteries. These smaller, muscular vessels play a crucial role in transporting blood to capillaries. The diameter of the arteriole lumen, the internal open space through which blood flows, typically ranges between 100 and 300 micrometers.
Venules, on the other hand, are small veins that collect blood from capillary beds and transport it to larger veins. With diameters ranging from approximately 8 to 100 micrometers, venules are responsible for directing deoxygenated blood back to the heart.
Inner Layer, Tunica Intima
Arteries and veins share a similar structure in terms of their layers, but each layer has distinct characteristics that enable these blood vessels to carry out their specific functions. The innermost layer, also known as the tunica intima or tunica interna, is composed of endothelium. In arteries, the endothelium appears wavy due to the presence of smooth muscle constriction, while in veins, it appears smooth. Additionally, the lining of arteries contains an elastic membrane to accommodate the larger size of these vessels and withstand the pressures generated by blood flow.