Stage 1: Damage to tissue or blood vessels activates clotting factors that activate other clotting factors, which leads to the production of prothrombinase. The activated factors are within white ovals, whereas the inactive precursors are shown as yellow ovals. See the next screen for the two pathways.
Stage 2: Prothrombin is activated by prothrom- binase to form thrombin.
Stage 3: Fibrinogen is activated by thrombin to form fibrin, which forms the clot.
