SBA — Single Best Answer · Review
Question 348
Physiology → Haematology
Classification
Question
SSBAQuestion Header
Both the intrinsic and extrinsic coagulation pathways have successfully generated prothrombin activator.
Question Stem
Which sequence most accurately describes the subsequent events leading towards a stable fibrin clot?
Options
A
Fibrinogen → prothrombin → thrombin → fibrin
B
Prothrombin → fibrin → thrombin → fibrinogen
C
Thrombin → prothrombin → fibrinogen → fibrin
D
Prothrombin → thrombin → fibrin → fibrinogen
E
Prothrombin → thrombin → fibrinogen to fibrin → fibrin polymerisation and stabilisation
Explanation
Prothrombin activator converts prothrombin to thrombin in the presence of calcium. Thrombin converts fibrinogen to fibrin. Fibrin monomers polymerise, and the fibrin meshwork is stabilised by factor XIII in the presence of calcium.
Option Validity
A) Prothrombin is converted to thrombin before thrombin converts fibrinogen to fibrin; fibrinogen does not initiate this sequence.
B) Fibrin formation follows generation of thrombin and cannot precede it in this sequence.
C) Prothrombin activator acts on prothrombin to form thrombin, not the reverse.
D) Fibrinogen is the precursor converted by thrombin into fibrin, so it cannot appear after fibrin in the sequence.
Further Reading
Saxena. Textbook for MRCOG-1. Physiology - Haematology - Coagulation Pathway, pp.70–71.