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The endothelium (pl.: endothelia) is a single layer of squamous endothelial cells that line the interior surface of blood vessels and lymphatic vessels. [1] The endothelium forms an interface between circulating blood or lymph in the lumen and the rest of the vessel wall.
Blood vessels function to transport blood to an animal's body tissues. In general, arteries and arterioles transport oxygenated blood from the lungs to the body and its organs, and veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels also circulate blood throughout the circulatory system.
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 lymphatic capillaries are described to be blind ended vessels (closed on one end), and they are made up of a single non-fenestrated layer of endothelial cells; The lymph capillaries function to aid in the uptake of fluids, macromolecules, and cells. Although they are generally similar to blood capillaries, the lymph capillaries have ...
Circulating endothelial cells (CECs) are endothelial cells that have been shed from the lining of the vascular wall into the blood stream. [1] Endothelial cells normally line blood vessels to maintain vascular integrity and permeability, but when these cells enter into the circulation, this could be a reflection of vascular dysfunction and damage. [2]
Normal blood vessel (left) vs. vasodilation (right) Vasodilation, also known as vasorelaxation, is the widening of blood vessels. [1] It results from relaxation of smooth muscle cells within the vessel walls, in particular in the large veins, large arteries, and smaller arterioles. [2]
It is very thin in veins and venules. [1] In elastic arteries such as the aorta, which have very regular elastic laminae between layers of smooth muscle cells in their tunica media, the internal elastic lamina is approximately the same thickness as the other elastic laminae that are normally present. [2]
High endothelial venules (HEV) are specialized post-capillary venules characterized by plump endothelial cells as opposed to the usual flatter endothelial cells found in regular venules. [1] HEVs enable lymphocytes circulating in the blood to directly enter a lymph node (by crossing through the HEV).