BIOC63H3 Lecture Notes - Lecture 8: Lymphatic Vessel, Microcirculation, Smooth Muscle Tissue

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14 Oct 2011
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The microcirculation comprises the smallest arterioles, and the exchange vessels, including the capillaries and the post-capillaries venules. Then transfer of gases, water, nutrients, waste materials and other substances between the blood and body tissues carried out by the exchange vessels is ultimate function of the cardiovascular system. Blood enters the microcirculation via small arterioles, the walls of which contain smooth muscle cells. These vessels are densely innervated by the sympathetic system, particularly in the splanchnic and cutaneous vascular beds. Sympathetically mediated constriction of each small arteriole reduces the blood-flow to many capillaries. In some cases tissues (e. g. mesentery) capillaries branch form thoroughfare vessels which run from small arterioles to venules (figure 1a, right). The proximal (arteriolar) end of such a vessel is termed metarteriole, and it is wrapped intermittently in smooth muscles cells. The capillaries have a ring of smooth muscle called a precapillary sphincter at the origin, but thereafter lack smooth muscle cells.

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