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Three initial responses to vascular injury:
- Vascular vasoconstriction
- Platelet adhesion
- Thrombin generation
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Intrinsic pathway:
- Exposed collagen + prekallikrein + HMW kininogen + factor XII ->
- XI ->
- IX + VIII ->
- Prothrombin to thrombin ->
- Fibrinogen to fibrin
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Extrinsic pathway:
- Tissue factor (injured cells) + factor VII ->
- X and V ->
- Prothrombin to thrombin ->
- Fibrinogen to fibrin
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Prothrombin complex
- X, V, Ca, platelet factor 3, and prothrombin
- Forms on platelets
- Catalyzes the formation of thrombin
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Antithrombin III
- Key to anticoagulation
- Binds and inhibits thrombin
- Inhibits factors IX, X, and XI
- Activated by heparin
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