Describe coagulation and the role that platelets play in the process

Describe coagulation and the role that platelets play in the process.

Clotting can be thought of as occurring in two phases: primary and secondary hemostasis. Primary hemostasis is the creation of the initial platelet plug and secondary hemo-stasis is the creation of the stable fibrin clot. Platelets play an important role in both processes. Generally, blood vessels prevent platelet adhesion by releasing a potent vasodilator, prostacyclin. After vessel wall injury, prostacy-clin levels decrease and platelets adhere to the vessel wall. Adhesion leads to activation and degranulation with release of adenosine-5-diphosphate (ADP), serotonin and thromboxane that leads to platelet aggregation. Further aggregation leads to formation of a platelet plug. This plug is unstable and requires fibrin formation, which occurs by activation of the intrinsic and/or extrinsic coagulation sys-tem. Platelets provide the phospholipid membrane upon which the coagulation cascade occurs. Platelet abnormali-ties can be qualitative or quantitative and are the most common hematologic disorders during pregnancy.