All blood vessels have four components, except capillaries which have only one (Figure 02). The aorta and other large arteries contain elastin fibers in the walls. Elastin is an exceedingly stretchy material, even more so than natural rubber. This fact is consistent with the Windkessel function of these vessels; that is, the elastin stretches readily under the influence of increased pressure during ventricular systole, storing energy. This potential energy is later given back during ventricular diastole, helping to maintain arterial blood pressure.
Arterioles have even more smooth muscle than arteries, consequently their walls are relatively thicker. Thus the lumen diameter : wall thickness ratio is smaller than that for arteries. The generous amount of smooth muscle is consistent with the microcirculatory control function of the arterioles.
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