Vasodilation

Vasodilation, also known as vasorelaxation, is the widening of <a href="/facts/Blood_vessel/FG3GjPNW">blood vessels</a>. It results from relaxation of <a href="/facts/Smooth_muscle/mpcpTsHp">smooth muscle</a> cells within the vessel walls, in particular in the large <a href="/facts/Vein/I6ycr6gF">veins</a>, large <a href="/facts/Artery/Y1Yj0jat">arteries</a>, and smaller <a href="/facts/Arteriole/HYVG0g7P">arterioles</a>. Blood vessel walls are composed of endothelial tissue and a basal membrane lining the lumen of the vessel, concentric smooth muscle layers on top of endothelial tissue, and an <a href="/facts/Adventitia/rSyJHUkx">adventitia</a> over the smooth muscle layers. Relaxation of the smooth muscle layer allows the blood vessel to dilate, as it is held in a semi-constricted state by sympathetic nervous system activity. Vasodilation is the opposite of <a href="/facts/Vasoconstriction/9hdY0aR2">vasoconstriction</a>, which is the narrowing of blood vessels.
When blood vessels dilate, the <a href="/facts/Blood_flow/HzubzJpn">flow of blood</a> is increased due to a decrease in <a href="/facts/Vascular_resistance/XPH12Hub">vascular resistance</a> and increase in <a href="/facts/Cardiac_output/7JCDn6Ht">cardiac output</a>. Vascular resistance is the amount of force circulating blood must overcome in order to allow <a href="/facts/Perfusion/EFVLNUTg">perfusion</a> of body tissues. Narrow vessels create more vascular resistance, while dilated vessels decrease vascular resistance. Vasodilation acts to increase cardiac output by decreasing <a href="/facts/Afterload/h5CGnv4r">afterload</a>, −one of the four determinants of cardiac output.
By expanding available area for blood to circulate, vasodilation decreases <a href="/facts/Blood_pressure/VtqqSM2J">blood pressure</a>. The response may be <a href="/facts/Intrinsic/5WJ1zN7q">intrinsic</a> (due to local processes in the surrounding <a href="/facts/Tissue_(biology)/H7CpML7A">tissue</a>) or <a href="/facts/Extrinsic/5WJ1zN7q">extrinsic</a> (due to <a href="/facts/Hormone/WFnBnINJ">hormones</a> or the <a href="/facts/Nervous_system/CDxRKU2U">nervous system</a>). In addition, the response may be localized to a specific <a href="/facts/Organ_(anatomy)/FUYsLaxz">organ</a> (depending on the <a href="/facts/Metabolism/WxDrm8k5">metabolic</a> needs of a particular tissue, as during strenuous exercise), or it may be systemic (seen throughout the entire <a href="/facts/Systemic_circulation/WXwudzzc">systemic circulation</a>).
<a href="/facts/Endogeny_(biology)/DFkSLkRI">Endogenous</a> substances and <a href="/facts/Drug/FFFUI9n4">drugs</a> that cause vasodilation are termed vasodilators. Many of these substances are <a href="/facts/Neurotransmitter/LlpYFSU3">neurotransmitters</a> released by perivascular nerves of the <a href="/facts/Autonomic_nervous_system/hdmEY1Ay">autonomic nervous system</a> <a href="/facts/Baroreceptor/WDLRp2vB">Baroreceptors</a> sense blood pressure and allow adaptation via the mechanisms of vasoconstriction or vasodilation to maintain <a href="/facts/Homeostasis/rloTGAHa">homeostasis</a>.

Vasodilation open-in-new

Vasodilation