Hemostasis: process of keeping blood within damaged vessel. Decreases blood flow and pressure to wounded area. Plug formed via platelet adhesion: stick to exposed collagen in damaged area, adhered platelets activate, release cytokines, reinforce local vasoconstriction, recruit more platelets. Exposed collagen and tissue factor initiate formation of fibrin: reinforces platelet plug, forming a clot, fibrin results from coagulation cascade (enzymatic reaction, chemical factors promote aggregation and adhesion. Plasmin dissolves fibrin as vessel heals, clot retracts. When blood vessel wall is damaged, collagen is exposed due to damaged endothelium, activating platelets. Binding activates platelets, degranulate, release vasoconstrictors and platelet aggregators: Psl301h1|lecture 5: serotonin, adp, platelet-activating factor (paf) Intact cells release nitric oxide and convert membrane lipids to prostacyclin. Coagulation converts a platelet plug into a clot. Damaged tissue exposes collagen: uses proteins already present in plasma, collagen activates factor xii to begin cascade. Damaged tissue exposes tissue thromboplastin/factor iii: activates factor vii, begins cascade.