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Abstract The endothelium consists of a monolayer of endothelial cells in the lumen of blood vessels. While it functions as a mechanical barrier, more importantly it maintains anti-inflammatory, anticoagulant properties, enables physiological control of vasoregulation, and modulates vascular permeability.The endothelial cells are exposed to a highly dynamic environment .Shear stress is a key regulator of endothelial cells. Shear stress is the tangential force derived by friction of the flowing blood on the endothelial surface.The fact that ECs respond to shear stress indicates that they have the ability to sense shear stress as a signal and transmit it into the interior of the cell .Vascular ECs are not only able to respond to flow but also respond differently to different types of flow.Laminar shear stress activates signaling pathways that induce endothelial elaboration of a number of factors that promote vasodilation and inhibit adherence of circulating blood elements. Several atheroprotective genes; antioxidant, anti-inflammatory, anticoagulant, and antiapoptotic genes, are up regulated by sustained laminar shear stress. In contrast, disturbed flow with a low shear stress elicits factors that impair vasodilation and increase adhesion of circulating blood elements. Also, several genes whose products may serve proinflammatory, procoagulant, proliferative, and proapoptotic functions, are upregulated. Solaminar shear stress plays protective roles; whereas alteration of EC biology by disturbed flow with low shear stress has the reverse effect . |