Coagulation cascade - factor roles
Core concept
- In vivo the cell-based model applies; the intrinsic/extrinsic waterfall survives only because it maps onto the lab tests
A. Initiation - on the TF-bearing cell
- Vascular injury exposes tissue factor (subendothelial fibroblasts, SMC)
- TF + VII -> TF:VIIa complex = the physiological trigger
- -> activates X (and IX)
- -> Xa + Va -> trace thrombin (too little to make clot)
B. Amplification - trace thrombin as the switch
- Activates platelets; activates V, VIII, XI
- Splits VIII off VWF
C. Propagation - on the activated platelet surface
- Tenase IXa + VIIIa -> Xa
- Prothrombinase Xa + Va -> thrombin burst
- Fibrinogen -> fibrin; XIIIa cross-links
3 more sections, plus exam facts
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