Coagulation Cascade — MFDS Part 1 MCQ

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ModeratePhysiologyCoagulation CascadeMFDS Part 1

During secondary haemostasis, the factor Xa–factor Va prothrombinase complex generates an activated serine protease. This protease cleaves fibrinopeptides A and B from fibrinogen, allowing fibrin monomers to form. Which activated factor is it?

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Correct answer: E — Thrombin (Factor IIa)

Thrombin (factor IIa) is the activated serine protease that cleaves fibrinopeptides A and B from fibrinogen, producing fibrin monomers that polymerise. Factor Xa acts one step earlier: with its cofactor, factor Va, it forms the prothrombinase complex that converts prothrombin to thrombin. Factor VIIa participates in the tissue factor pathway and activates factors IX and X. Factor XIIIa acts after fibrin formation as a transglutaminase, covalently cross-linking fibrin to strengthen and stabilise the clot. Factor Va is an essential non-enzymatic cofactor within prothrombinase rather than the protease that cleaves fibrinogen.

Reference: Wolberg AS. Fibrinogen and fibrin: synthesis, structure, and function in health and disease. Journal of Thrombosis and Haemostasis. 2023;21(11):3005–3015. https://pubmed.ncbi.nlm.nih.gov/37625698/