Figure 121

Schematic diagram of the major structural features of blood vessels.

The layers or tunics of the blood vessel walls are labeled in the upper two panels. The arrangement of the microcirculatory bed in certain parts of the body is shown in the lowest panel. Note the location of pericytes and their relationship to the basal lamina. Also, an arteriovenous (A.V.) anastomosis is shown within the microcirculatory bed. t., tunica. (Based on Rhodin JAG. Handbook of Physiology. New York: Oxford University Press, 1980.)

S? general features of arteries and veins

The walls of arteries and veins are composed of three layers called tunics

The three layers of the vascular wall, from the lumen outward (see Fig. 12.1), are

• Tunica intima, the innermost layer of the vessel. It consists of three components: (a) a single layer of squamous epithelial cells, the endothelium; (b) the basal lamina of the endothelial cells; and (c) the sub endothelial layer, consisting of loose connective tissue. Occasional smooth muscle cells are found in the loose connective tissue. The

media t. adventitia

V<f . pericyte V capillaries covered byT

endothelial

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