Platelet Physiology.

Platelets are anucleate circulating blood particles. They circulate around the body in an inactive state until they come into contact with areas of endothelial damage or activation of the coagulation cascade. Here they adhere to the endothelial defect, change shape, release their granule contents, and stick together to form aggregates. Physiologically these processes help to limit blood loss; however, inappropriate or excessive platelet activation results in an acute obstruction of blood flow, as occurs, for example, in an acute myocardial infarction. However, activated platelets also express and release molecules that stimulate a localized inflammatory response through the activation of leukocytes and endothelial cells, and it is now clear that platelet function is not merely limited to the prevention of blood loss. Indeed, platelets have been implicated in many pathological processes including host defense, inflammatory arthritis, adult respiratory distress syndrome, and tumor growth and metastasis. In this chapter I review our current understanding of platelet physiology in order to provide a global background for the more in-depth focused chapters later in this book. [ABSTRACT FROM AUTHOR]