Large arteries are of two kinds , conducting /elastic arteries and muscular/distributive arteries. Arterioles are very small arteries which branch to form capillaries' 1. The large elastic arteries are located near the heart. Some examples are the aorta, brachiocephalic, the subclavian and the brachial Elastic arteries have all three layers or tunics namely, Tunica externa, tunica media and tunica intima (endothelial layer). There are elastic fibers in all three layers with the tunica media having the most. Elastic arteries expand when a heart pulse contraction pushes blood into them . Their great compliance enable them to told the extra volume of blood. When the heart relaxes the large elastic arteries recoil and slowly and smoothly maintain the even transfer of blood to the muscular arteries. Although the elastic arteries have smooth muscle fibers they do not contract significantly to alter blood flow . They serve mainly as tubes that allow blood to flow in a largely no-pulsatile manner to the muscular distributing arteries. 2.Muscular arteries; are second id in in diameter.. Their main function is to distribute blood to the organs, therefore there is a renal artery, a splenic artery, a hepatic artery . These arteries have all three tunic but in these the tunica media is thich with more smooth muscle and less elastic than is found in tunica media of elastic arteries.. These arteries do have an elastic membrane on the inner and outer surface of the tunica media. Muscular arteries are active in controlling blood flow by muscular contraction and relaxation of the arterial walls. 3.Arterioles are the smallest arteries with diameters of 0.3mm to 10 uM. Lrger arterioles have all three tunics ( layers) tunica externa, tunic media and tunica interna, The tunica in these arterioles is mainly of smooth muscle cells with sparse elastic fibers. Small arterioles are essentially just endothelial tubes with a few smooth muscle tubes wrapped around them. Arteriole serve the important function of controlling the amount of blood that flows into a capillary bed or network. Contraction of the arteriole keeps blood (shunts it) away from a capillary bed. Relaxation of an arteriole allows blood to flow into a capillary bed and supply the relevant organ.
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Elatic arteries are large arteries near the heart. . They have wide lumina with diameters of 2.5-1.0cm. The large arteries have all three tunics and much elatic tissue. They are able to expand in respose to the pumping action of the heart and retain extra volume of blood without initiating pulses in the blood flow. Their large diameters, great compliance and sturdy thich walls eable the elatic arteries to funtion much like pipes that essetially just pass on blood to the muscular arteries. Muscular arteries also have all three tunics but have more smooth muscle cells and less elastic fibers in their tunica media than do elastic arteries. However, muscular /distributive arteries do have elastic membranes bordering the tunica media. The muscular arteries distribute blood to organs; examples are renal artery, splenic artery, superior mesenteric, radial artery. In muscular arteries the tunica externa( adventia) is the thickest layer. Arterioles are very small vessels with diameters of 0.3mm to 10um. Like capillaries arterioles are sometimes called called resistance vessels because the small dimeters of their narrow lumina offer resistance to blood flow. Some , larger arterioles have all three tunics, but the smaller arterioles are essentially endothelial tubes with a few smooth muscle cells wrapped around them. Arterioles give rise to capillaries or branch to for capillary beds. By contraction and relaxation arterioles can control the amount of blood that is allowed to flow through a capillary bed.