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Question 300
Physiology → Haematology
Classification
Question
SSBAOptions
Explanation
After thrombin converts fibrinogen into fibrin, fibrin polymerises. factor XIII together with calcium produces the stable fibrin mesh. Earlier coagulation steps may therefore occur while final stabilisation remains impaired.
Option Validity
A) Factor VII is associated with the extrinsic pathway, while vitamin K is required by the liver for prothrombin and other coagulation factors. This is not the combination specified for stabilising the fibrin mesh.
B) Collagen initiates the intrinsic pathway through factor XII. This occurs upstream of fibrin formation and is not the final fibrin-stabilisation step.
C) Platelets and serotonin contribute to primary haemostasis and vascular responses. They are not the factor-calcium combination identified for production of the stable fibrin mesh.
D) Prothrombin is converted to thrombin after formation of prothrombin activator, while tissue thromboplastin initiates the extrinsic pathway. This does not represent the final stabilisation step.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Blood Coagulation, pp.70-71.