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Write a 6 page essay on Vasodilation and Vasoconstriction.

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Hence, it becomes necessary for the tissues to control the blood they receive according to their necessities under a range of situations. Various organ tissues have different requirements. For instance, blood flow to skin is important for heat loss from the body. This is a significant step in the thermoregulatory functions of the body (Guyton &amp. Hall, 2006). Vasoconstriction and vasodilation are two very fundamental and significant processes that are involved in controlling the amount of blood flow through a rapid and quick response under different body conditions and are brought about by a sequence of events and various mediators. Vasodilation and vasoconstriction is explained by various theories formulated in response to the body needs and metabolic conditions. Humoral control of the circulatory function is also an important regulator of vasodilation and vasoconstriction. The arterioles consist of small amount of elastic tissue which is lacking in the arteries. But, like arteries, they do consist of a thick layer of smooth muscle which is supplied by a large amount of sympathetic nerve fibres regulating the constriction and dilation. The smooth muscles also respond to other stimuli such as hormones, mechanical stretch and other local chemical changes. When smooth muscles of the arterioles are stimulated by the nerve fibers or by the other local chemical changes, the vessel circumference reduces and narrows because of the contraction of the smooth muscles surrounding the vessel circularly. This narrowing of the vessels is described as vasoconstriction and results in increased resistance and decreased blood flow to the target organs and tissues. Vasodilation, on the other hand, is the increase in the circumference of the blood vessel and is brought about by the relaxation of the smooth muscles of the arterioles. The enlargement of the vascular circumference causes reduced resistance to blood flow and thus increasing the flow to the target organs (Sherwood 2012). Apart from the vasodilation and vasoconstriction process which is achieved as a response to various stimuli, the arteriolar smooth muscles maintain a continuous state of contractility which is termed as “vascular tone”. Vascular tone is maintained by the myogenic capability of the smooth muscles which is self-induced and is not aided by any hormonal activity or sympathetic innervations. Second important factor that maintains vascular tone is the sympathetic nerve fibre innervations of the smooth muscles. These fibres are responsible for releasing nor-epinephrine, an important vasoconstrictor, for increasing the vascular tone (Sherwood 2012). The maintenance of vascular tone as an ongoing process is significant as the increase or decrease in vascular tone helps in achieving vasoconstriction and vasodilation, respectively. However, the factors that lead to the vasodilation and vasoconstriction are grouped into two categories- intrinsic controls and extrinsic controls. The former factors determine the distribution of cardiac output through vascular tone regulation while the extrinsic factors regulate the blood pressure (Sherwood 2012).

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