For blood clotting fibrinogen is changed into fibrin with the help of?

DHS 2018 shift 1st

Applied Physiology

Easy

Appeared in: DHS 2018 shift 1st

Explanation

Thrombin is the active enzyme (Factor IIa) responsible for the final step of clot formation.
It acts specifically on fibrinogen (Factor I), a soluble plasma protein.
Thrombin cleaves fibrinogen into fibrin monomers, which then polymerize to form an insoluble fibrin mesh, the structural basis of a blood clot.
This conversion is the central event of the final common pathway of coagulation.

Option A: Antithrombin is an anticoagulant; its function is to inactivate thrombin and other clotting factors, thus preventing clot formation. It has the opposite effect of what the question asks.
Option C: Platelets are essential for primary hemostasis (forming the initial plug) and provide a phospholipid surface for the coagulation cascade, but they do not directly convert fibrinogen to fibrin.
Option D: Vitamin K is a necessary cofactor for the synthesis of several clotting factors (Prothrombin/Factor II, VII, IX, X) in the liver. It is an upstream requirement for the cascade but does not participate directly in the final fibrinogen-to-fibrin conversion.

Clinical Relevance

Nursing practice connection: Knowing The final common pathway of the blood coagulation cascade helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Understanding this step is crucial for interpreting coagulation studies like Prothrombin Time (PT), International Normalized Ratio (INR), and Activated Partial Thromboplastin Time (aPTT), which assess the integrity of the clotting cascade.
Nurses administer anticoagulant medications like heparin (which enhances antithrombin activity) and warfarin (a Vitamin K antagonist). Knowing the mechanism helps in monitoring for therapeutic effects and risks like bleeding.
In conditions like Disseminated Intravascular Coagulation (DIC), there is widespread activation of thrombin, leading to excessive fibrin formation and consumption of clotting factors, resulting in both thrombosis and hemorrhage.

How to Approach the Question

First, identify the core process in the question: the conversion of 'fibrinogen' to 'fibrin'.
Recall the steps of the blood coagulation cascade. Remember it has three main stages: formation of prothrombin activator, conversion of prothrombin to thrombin, and conversion of fibrinogen to fibrin.
Focus on the final step. The name of the enzyme often gives a clue to its substrate. 'Thrombin' acts on 'prothrombin' (its precursor) and is the key to the final clot.
Evaluate each option based on its known role in hemostasis. Eliminate options that are inhibitors (antithrombin), involved in earlier stages (platelets), or necessary for synthesis rather than direct action (Vitamin K).

Concept Tested & Keywords

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E6 Physiology Essentials Sembulingam 10e Part 1 p. 137-139

E6 Harper's Illustrated Biochemistry2023 (pp 26-793 of 813) p. 667-669