In the coagulation process, which enzyme converts inactive fibrinogen to insoluble fibrin threads? & x20; - RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, PB B.Sc Nursing Entrance-2019

Explanation

Thrombin is the active serine protease enzyme that catalyzes the conversion of soluble fibrinogen (Factor I) into insoluble fibrin monomers.
This reaction is the final, pivotal step of the common pathway in the coagulation cascade, leading directly to clot formation.
The resulting fibrin monomers polymerize and are cross-linked by Factor XIIIa to form a stable fibrin mesh, which constitutes the structural basis of a blood clot.

Option A: Prothrombin activator is a complex of activated factors that functions one step earlier in the cascade. Its role is to convert prothrombin into thrombin.
Option B: Prothrombin (Factor II) is an inactive zymogen, or precursor protein. It is not an active enzyme and cannot act on fibrinogen until it is converted into thrombin.
Option D: Thromboplastin, also known as Tissue Factor (Factor III), is an initiator of the extrinsic pathway. It is released from damaged cells and helps activate Factor X, but it does not directly interact with fibrinogen.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Physiology of the blood coagulation cascade as background academic context rather than a clinical decision trigger.
Understanding the role of thrombin is crucial for nurses administering anticoagulant medications. Direct thrombin inhibitors (e.g., dabigatran) work by directly blocking this enzyme's activity to prevent clot formation.
Nurses may monitor coagulation studies like Thrombin Time (TT), which directly measures the time it takes for a clot to form in a plasma sample after adding thrombin. A prolonged TT can indicate a fibrinogen deficiency or the presence of thrombin inhibitors.
What if? A patient has severe liver disease? The liver is the primary site for synthesis of most clotting factors, including prothrombin (Factor II) and fibrinogen (Factor I). In severe liver disease, their production is impaired, which disrupts the entire cascade and significantly increases the patient's risk of uncontrolled bleeding.

How to Approach the Question

First, identify the core of the question, which is asking for the specific enzyme that converts 'fibrinogen' into 'fibrin'.
Recall the three fundamental stages of the blood coagulation cascade.
Mentally review Stage 1: Formation of Prothrombin Activator.
Review Stage 2: The conversion of Prothrombin to Thrombin by prothrombin activator.
Review Stage 3: The conversion of Fibrinogen to Fibrin. The enzyme responsible for this step is Thrombin.
Compare this knowledge with the given options and select 'Thrombin' as the correct answer.

Concept Tested & Keywords

Concept Tested: Physiology of the blood coagulation cascade
Stem keywords: coagulation process, enzyme, inactive fibrinogen, insoluble fibrin threads
Lead-in keywords: which enzyme
Negative lead-in flag: false

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