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A precapillary sphincter is a band of contractile mural cells either classified as smooth muscle or pericytes that adjusts blood flow into capillaries.They were originally described in the mesenteric microcirculation, and were thought to only reside there.
Vasoconstriction affects flow rate and surface properties of the microvasculature by constricting the smooth muscle cells and decreasing the diameter of flow. The smooth muscle cells are able to constrict from both external and internal stimuli. This mechanism can be triggered by the ambient temperature or the autonomic nervous system. [7]
A metarteriole is a short microvessel in the microcirculation that links arterioles and capillaries. [1] Instead of a continuous tunica media, they have individual smooth muscle cells placed a short distance apart, each forming a precapillary sphincter that encircles the entrance to that capillary bed. Constriction of these sphincters reduces ...
Vascular smooth muscle cells also play important roles during development, e.g. driving osteocyte differentiation from undifferentiated precursors during osteogenesis. [1] Arteries have a great deal more smooth muscle within their walls than veins, thus their greater wall thickness. This is because they have to carry pumped blood away from the ...
Arterioles carry the blood to the capillaries, which are not innervated, have no smooth muscle, and are about 5-8 μm in diameter. Blood flows out of the capillaries into the venules, which have little smooth muscle and are 10-200 μm. The blood flows from the venules into the veins.
Lymph vessels are lined by endothelial cells, and have a thin layer of smooth muscle, and adventitia that binds the lymph vessels to the surrounding tissue. Lymph vessels are devoted to the propulsion of the lymph from the lymph capillaries, which are mainly concerned with the absorption of interstitial fluid from the tissues.
Mural cells are the vascular smooth muscle cells (vSMCs), and pericytes, of the microcirculation.Both types are in close contact with the endothelial cells lining the capillaries, and are important for vascular development and stability.
Smooth muscle is grouped into two types: single-unit smooth muscle, also known as visceral smooth muscle, and multiunit smooth muscle. Most smooth muscle is of the single-unit type, and is found in the walls of most internal organs (viscera); and lines blood vessels (except large elastic arteries), the urinary tract , and the digestive tract .