ROLE OF ENDOTHELIUM IN THROMBOSIS AND HEMOSTASIS

Vascular endothelium is strategically located at the interface between tissue and blood. It is pivotal for protecting against vascular injur y and maintaining blood fluidity. Normal endothelium releases prostacy clin and nitric oxide, potent inhibitors of platelet and monocyte acti vation and vasodilators. Their syntheses are governed by isoforms of e nzymes. Normal endothelial surface expresses ecto-adenosine diphosphat ase, which degrades adenosine diphosphate and inhibits platelet aggreg ation; thrombomodulin, which serves as a binding site for thrombin to activate protein C; and heparin-like molecules, which serve as a cofac tor for antithrombin III. Normal endothelium secretes tissue plasminog en activator, which activates the fibrinolysis system. Endothelium pro duces and secretes von Willebrand factor, which mediates platelet adhe sion and shear-stress-induced aggregation. Injury to endothelium is ac companied by loss of protective molecules and expression of adhesive m olecules, procoagulant activities, and mitogenic factors, leading to d evelopment of thrombosis, smooth muscle cell migration, and proliferat ion and atherosclerosis.