Editing Platelet (section)

====Trigger (induction)====
Platelet activation begins seconds after adhesion occurs. It is triggered when ''collagen'' from the subendothelium binds with its receptors ([[GPVI]] receptor and integrin α2β1) on the platelet. GPVI is associated with the Fc receptor gamma chain and leads via the activation of a tyrosine kinase cascade finally to the activation of PLC-gamma2 ([[PLCG2]]) and more calcium release.{{citation needed|date=December 2021}}

[[Tissue factor]] also binds to [[factor VII]] in the blood, which initiates the extrinsic [[coagulation]] cascade to increase [[thrombin]] production. Thrombin is a potent platelet activator, acting through Gq and G12. These are [[G protein-coupled receptor]]s and they turn on calcium-mediated [[signaling pathways]] within the platelet, overcoming the baseline calcium efflux. Families of three G proteins (Gq, Gi, G12) operate together for full activation. Thrombin also promotes secondary fibrin-reinforcement of the [[platelet plug]]. Platelet activation in turn degranulates and releases [[factor V]] and [[fibrinogen]], potentiating the coagulation cascade. Platelet plugging and coagulation occur simultaneously, with each inducing the other to form the final fibrin-crosslinked thrombus.{{citation needed|date=December 2021}}