Local tissues in hemostasis and platelet review

Abstract

Hemostasis is a complex physiologic state able to change rapidly depending on the needs of the organism. The hemostatic system broadly consists of three essential elements: local (vascular) tissues, platelets, and biochemical factors. In health, these three elements maintain a state of neutrality (or mild antithrombosis) to prevent pathologic intravascular clotting. When needed to stop hemorrhage at a site of injury, the hemostatic system rapidly allows for a powerful prothrombotic response at the site of injury while maintaining neutrality throughout the remainder of the organism. Maintaining the appropriate state of hemostasis begins with the very tissues in which the blood circulates-blood vessels. Endothelium, which lines the vessels, and subendothelial structures are physiologically active in hemostasis. When uninjured and in a non-pathologic state, the endothelium allows blood to remain in a fluid state, preventing pathologic intravascular thrombosis. With vessel injury, the endothelium and subendothelial tissues are responsible for initiating the explosion of pro-hemostatic responses culminating in clotting and cessation of bleeding. The second component of hemostasis, the platelet, also fluctuates from neutral to prothrombotic states. With hemorrhage, platelets become the essential mediators that anchor the procoagulant reactions to the site of vascular injury, leading to local thrombus formation and the cessation of bleeding. This chapter reviews the fundamental physiology and pathophysiology of local tissues and platelets in hemostasis. This knowledge is essential for understanding diseases and management of patients with bleeding disorders attributed to local tissues and platelets and the pharmacology of current and developing antiplatelet medications.