Platelets adhere to collagen (by vwf plasma protein), changes its conformation, and become able to bind to platelets. o binding of platelets to collagen triggers the platelets to release the contents of their secretory vesicles which contains agents, that act to induce multiple changes in metabolism, shape, and surface proteins through platelet activation (this also synthesizes thromboxane a2, which stimulates platelet aggregation). It consists mainly of fibrin o the activated platelets also display particular phospholipids, called platelet factor, which functions as a cofactor in the steps mediated by the bound clotting factors. o prothrombin is converted to thrombin which catalyzes the reaction in which polypeptides are split from fibrinogen. The erythrocytes get trapped in the fibrin, forming the clot: clotting cascade o intrinsic pathway everything is in the blood first plasma protein factor xii is activated to factor xiia , which then catalyzes the activation of factor xi to xia, which activates factor ix to ixa.