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Layers of vein wall shown in comparison to arterial wall. There are three sizes of vein, large, medium, and small. Smaller veins are called venules. The smallest veins are the post-capillary venules. Veins have a similar three-layered structure to arteries. The layers known as tunicae have a
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 endothelial cells are in direct contact with the blood flow.
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 ...
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 superior vena cava is made up of three layers, starting with the innermost endothelial tunica intima. The middle layer is the tunica media, composed of smooth muscle tissue, and the outermost and thickest layer is the tunica adventitia, composed of collagen and elastic connective tissue that allow for flexibility.
This is normally the thickest tunic in veins and may be thicker than the tunica media in some larger arteries. The outer layers of the tunica externa are not distinct but rather blend with the surrounding connective tissue outside the vessel, helping to hold the vessel in relative position. [3]
Venous vasa vasorae, that originate within the vessel wall of the artery but then drain into the main lumen or branches of concomitant vein. [1] Depending on the type of vasa vasorum, it penetrates the vessel wall starting at the intimal layer (vasa vasorum interna) or the adventitial layer (vasa vasorum externa). Due to higher radial and ...
Post-capillary venules are the smallest of the veins with a diameter of between 10 and 30 micrometres (μm). When the post-capillary venules increase in diameter to 50μm they can incorporate smooth muscle and are known as muscular venules. [1] Veins contain approximately 70% of total blood volume, while about 25% is contained in the venules. [2]