Which substance initiates the extrinsic coagulation pathway?

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Multiple Choice

Which substance initiates the extrinsic coagulation pathway?

Initiation of the extrinsic coagulation pathway occurs when tissue factor, also known as thromboplastin and a cellular component (Factor III), is exposed to circulating blood at a vascular injury. Tissue factor binds to and activates factor VII to VIIa, forming the TF–VIIa complex. This complex then activates factor X to Xa (and can also activate IX to IXa), triggering the rapid start of thrombin generation and downstream fibrin formation. The extrinsic pathway is thus driven by tissue factor exposure, linking injury to coagulation. The other factors are associated with the intrinsic pathway or contact activation: Factor VIII is a cofactor in the intrinsic tenase complex, Factor IX participates in intrinsic pathway steps, and Factor XII initiates the contact pathway. They are not the initiators of the extrinsic pathway.

Initiation of the extrinsic coagulation pathway occurs when tissue factor, also known as thromboplastin and a cellular component (Factor III), is exposed to circulating blood at a vascular injury. Tissue factor binds to and activates factor VII to VIIa, forming the TF–VIIa complex. This complex then activates factor X to Xa (and can also activate IX to IXa), triggering the rapid start of thrombin generation and downstream fibrin formation. The extrinsic pathway is thus driven by tissue factor exposure, linking injury to coagulation.

The other factors are associated with the intrinsic pathway or contact activation: Factor VIII is a cofactor in the intrinsic tenase complex, Factor IX participates in intrinsic pathway steps, and Factor XII initiates the contact pathway. They are not the initiators of the extrinsic pathway.

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