Endothelium

The endothelium is the thin layer of cells that lines the interior surface of blood vessels, forming an interface between circulating blood in the lumen and the rest of the vessel wall. These cells are called endothelial cells. Endothelial cells line the entire circulatory system, from the heart to the smallest capillary. These cells reduce turbulence of the flow of blood, allowing the fluid to be pumped farther.

Endothelial tissue is an epithelial tissue.

The endothelium normally provides a non-thrombogenic surface because it contains heparan sulfate which acts as a cofactor for activating antithrombin III, a protease that inactivates several factors in the coagulation cascade.

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