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The tunica media may (especially in arteries) be rich in vascular smooth muscle, which controls the caliber of the vessel. Veins do not have the external elastic lamina, but only an internal one. The tunica media is thicker in the arteries rather than the veins. The outer layer is the tunica adventitia and the thickest layer in veins. It is ...
The middle coat is composed of a thick layer of connective tissue with elastic fibers, intermixed, in some veins, with a transverse layer of muscular tissue. [6] The white fibrous element is in considerable excess, and the elastic fibers are in much smaller proportion in the veins than in the arteries.
The tunica intima (Neo-Latin "inner coat"), or intima for short, is the innermost tunica (layer) of an artery or vein. It is made up of one layer of endothelial cells (and macrophages in areas of disturbed blood flow), [ 1 ] [ 2 ] and is supported by an internal elastic lamina .
The tunica media in the veins is much thinner than that in the arteries as the veins are not subject to the high systolic pressures that the arteries are. There are valves present in many veins that maintain unidirectional flow. Unlike arteries, the precise location of veins varies among individuals. [5] [page needed]
In the smallest vessels, the vessels' own circulation nourishes the walls directly and they have no vasa vasorum at all. Vasa vasorum are more frequent in veins than arteries. [2] Some authorities hypothesize that the vasa vasorum would be more abundant in large veins, as partial oxygen pressure and osmotic pressure is lower in veins. This ...
Endothelium lines the inner wall of vessels, shown here. Microscopic view showing endothelium (at top) inside the heart. The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall. This forms a barrier between vessels and tissues and control the flow of substances and fluid into and out of ...
In the cases of veins or arteries, traumatic fistulas usually occur between artery and vein. Portacaval anastomosis , by contrast, is a veno-venous anastomosis between a vein of the portal circulation and a vein of the systemic circulation , which allows blood to bypass the liver in patients with portal hypertension , often resulting in ...
It is mainly composed of collagen and, in arteries, is supported by external elastic lamina. The collagen serves to anchor the blood vessel to nearby organs, giving it stability. The three layers of the blood vessels are: an inner tunica intima, a middle tunica media, and an outer tunica externa.