In the cellular-based model of coagulation, what occurs during the initiation phase?

In the cellular-based model of coagulation, what occurs during the initiation phase?

• A. Platelets and Cofactors Are Activated
• B. It Occurs on a Tissue Factor Bearing Cell
• C. Large Amounts of Thrombin Are Generated
• D. Fibrinogen Is Converted to Fibrin

Answer: (B)

During initiation, coagulation is triggered on tissue factor–bearing surfaces. Tissue factor binds activated factor VII (VIIa), forming the TF–VIIa complex, which then activates factor X to Xa and factor IX to IXa. This sequence generates a small amount of thrombin that starts the cascade and primes platelets and cofactors for the next phase, but does not produce a large thrombin burst or fibrin yet. Large thrombin generation and fibrin formation occur later in the propagation/activation steps.

During initiation, coagulation is triggered on tissue factor–bearing surfaces. Tissue factor binds activated factor VII (VIIa), forming the TF–VIIa complex, which then activates factor X to Xa and factor IX to IXa. This sequence generates a small amount of thrombin that starts the cascade and primes platelets and cofactors for the next phase, but does not produce a large thrombin burst or fibrin yet. Large thrombin generation and fibrin formation occur later in the propagation/activation steps.