**4. Extrinsic pathway**

The "Extrinsic Pathway" is initiated when endothelial injury causes tissue factor (TF, or FIII) to come into contact with FVII. TF non-proteolytically activates FVII. The FVIIa/TF complex then activates FX. The extrinsic pathway can be measured by the Prothrombin Time (PT) laboratory test.
