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You'll remember that the platelets attached to the injury and that their surfaces changed to become 'spiky'. They began to expose some of the phospholipids in their membranes, and clotting factors began to attach to those phospholipids.
While the intrinsic and extrinsic pathways are going on, the clotting factors that will turn into thrombin have attached to the platelets. When the complex of proteins formed by either clotting pathway also contacts the platelets, the prothrombin will turn to thrombin. It will begin to make fibrin, and the fibrin filaments will attach to the platelets to form the clot (King and Marchesini, 2004).
Deficiencies in any of the proteins in this pathway can cause hemophilia, or increased bleeding. The commonest form of hemophilia, Hemophilia A, is a Factor VIII deficiency.