Fibrinolysis — MFDS Part 1 MCQ

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ModeratePhysiologyFibrinolysisMFDS Part 1

Following formation of a stable cross-linked fibrin clot, tissue plasminogen activator converts plasminogen to its active form. Which haemostatic protein then directly cleaves fibrin during physiological fibrinolysis?

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Correct answer: E — Plasmin

Plasmin directly cleaves the fibrin network into soluble fibrin-degradation products and is therefore the principal effector enzyme of fibrinolysis. It is generated from circulating plasminogen by plasminogen activators, particularly tissue plasminogen activator. Thrombin instead converts fibrinogen into fibrin and promotes clot formation. Activated factor XIII stabilises the clot by cross-linking fibrin. Activated protein C limits coagulation by proteolytically inactivating factors Va and VIIIa rather than degrading fibrin. Antithrombin is a physiological inhibitor of coagulation proteases, especially thrombin and factor Xa, and is not the enzyme responsible for clot dissolution.

Reference: Mutch NJ, Medcalf RL. The fibrinolysis renaissance. Journal of Thrombosis and Haemostasis. 2023;21(12):3304-3316. https://pubmed.ncbi.nlm.nih.gov/38000850/