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The smallest veins are the post-capillary venules. Veins have a similar three-layered structure to arteries. The layers known as tunicae have a concentric arrangement that forms the wall of the vessel. The outer layer, is a thick layer of connective tissue called the tunica externa or adventitia; this layer is absent in the post-capillary ...
The muscle fiber cells are arranged in 5 to 7 layers of circular and longitudinal smooth muscle with about 50μ in length and contain well-marked, rod-shaped nuclei, which are often slightly curved. Separating the tunica media from the outer tunica externa in larger arteries is the external elastic membrane (also called the external elastic ...
The three layers of a blood vessel are an inner layer (the tunica intima), a middle layer (the tunica media), and an outer layer (the tunica externa). In dissection , the inner coat (tunica intima) can be separated from the middle (tunica media) by a little maceration, or it may be stripped off in small pieces; but, because of its friability ...
The tunica externa (Neo-Latin "outer coat"), also known as the tunica adventitia (Neo-Latin "additional coat"), [1] [2] is the outermost tunica (layer) of a blood vessel, surrounding the tunica media. It is mainly composed of collagen and, in arteries, is supported by external elastic lamina. The collagen serves to anchor the blood vessel to ...
Due to higher radial and circumferential pressures within the vessel wall layers closer to the main lumen of the artery, vasa vasorum externa cannot perfuse these regions of the vessel wall (occlusive pressure). The structure of the vasa vasorum varies with the size, function and location of the vessels. Cells need to be within a few cell ...
The middle layer is poorly developed so that venules have thinner walls than arterioles. They are porous so that fluid and blood cells can move easily from the bloodstream through their walls. Short portal venules between the posterior pituitary and the anterior pituitary lobes provide an avenue for rapid hormonal exchange via the blood. [3]
They are composed of only the tunica intima (the innermost layer of an artery or vein), consisting of a thin wall of simple squamous endothelial cells. [2] They are the site of the exchange of many substances from the surrounding interstitial fluid , and they convey blood from the smallest branches of the arteries ( arterioles ) to those of the ...
The middle layer is thicker in the arteries than it is in the veins: [6] The inner layer, tunica intima , is the thinnest layer. It is a single layer of flat cells ( simple squamous epithelium ) glued by a polysaccharide intercellular matrix, surrounded by a thin layer of subendothelial connective tissue interlaced with a number of circularly ...