Platelet induced hemostasis following injury is by all except
When the vessel wall is injured platelets adhere to the vessel wall by exposed collagen and Von Willebrand factor. Von Willebrand factor is a large circulating molecule in the blood produced by endothelium. Binding with platelets induces degranulation of platelets. Released granules, release ADP, which acts on ADP receptors inducing further aggregation of platelets. There are three types of ADP receptors P2Y1, P2Y2 , and P2X1. Most of the antiplatelet drugs used in Stroke and Ischemic heart disease act on this receptor
Platelet aggregation is also induced by platelet activation factor (PAF) secreted by neutrophil and monocyte and platelets. This also has an inflammatory activity. This acts by G-Protein coupled receptors which induce production of thromboxane A2 which induces platelet aggregation.
Prostacyclin has an anti aggregating effect on the platelet.
Serotonin released by platelet is vasoconstrictor thus it reduces bleeding.