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Blood vessels, especially their endothelial lining, play a critical role in the maintenance of vascular fluidity, arrest of hemorrhage (hemostasis), prevention of occlusive vascular phenomena (thrombosis), and regulation of inflammatory cell processes.* The endothelium extends to all recesses of the body and maintains an intimate association with flowing blood and blood cells. However, endothelial cell morphologies, gene-expression profiles, and functions vary among different vascular beds. For example, in straight arterial segments, but not at branch points or curvatures of the arteries or veins, endothelial cells align themselves in parallel to the direction of blood flow. Similarly, endothelial cells in post capillary venules are primarily responsible for mediating adhesion and transmigration of leukocytes, whereas arteriolar endothelium is important for regulation of vasomotor tone. Proteomic studies have revealed that endothelial cells have the unique capacity to express and elaborate thromboregulatory molecules, which can be classified according to their chronologic appearance following vascular injury. Early thromboregulators appear prior to thrombin formation and late thromboregulators arrive after thrombin has formed. This chapter reviews some of the mechanisms by which the vascular wall regulates hemostasis, and discuss their implications for vascular health and disease (Table 115–1).

Acronyms and Abbreviations

APC, activated protein C; Apo, apolipoprotein; APS, antiphospholipid syndrome; C5a, complement factor 5a; CAM, cell adhesion molecule; COX, cyclooxygenase; DAG, diacylglycerol; DDAVP, deamino D-arginine vasopressin; EPCR, endothelial protein C receptor; GMP, guanosine monophosphate; IL, interleukin; IP3, inositol triphosphate; Lp(a), lipoprotein(a); NFκB, nuclear factor kappa B; NO, nitric oxide; NOS, nitric oxide synthase; PAF, platelet-activating factor; PDGF, platelet-derived growth factor; PECAM, platelet endothelial cell adhesion molecule; PGI2, prostacyclin; PGIS, prostacyclin synthase; PSGL, P-selectin glycoprotein ligand; scu-PA, single-chain urokinase-type plasminogen activator; TAFI, thrombin-activatable fibrinolysis inhibitor; TF, tissue factor; TFPI, tissue factor pathway inhibitor; TM, thrombomodulin; TNF, tumor necrosis factor; t-PA, tissue-type plasminogen activator; VWF, von Willebrand factor.

Table 115–1.Chronology of Endothelial Cell Thromboregulators
Table 115–2.Early Pro- and Antithrombotic Thromboregulators Associated with Human Endothelial Cells

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