During clotting, the prothrombin is changed into thrombin in the presence of?

RUHS, Jaipur, M.Sc Nursing Entrance Exam-2015

Applied Physiology

Easy

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2015

Explanation

The correct option is 'Calcium ion and thromboplastin' because both are essential for the conversion of prothrombin to thrombin.
Calcium ions (Factor IV) act as a direct cofactor for the enzyme prothrombin activator, which catalyzes the conversion.
Thromboplastin (Factor III or Tissue Factor) is released from damaged tissue and initiates the extrinsic pathway of coagulation.
This extrinsic pathway leads to the formation of prothrombin activator, the enzyme complex necessary to convert prothrombin to thrombin.

Option A: Fibrinogen is the substrate that is converted into fibrin by thrombin in the final stage of clotting. It is not a cofactor for the formation of thrombin.
Option B: Vitamin K is essential for the synthesis of prothrombin (and factors VII, IX, X) in the liver. It is not directly involved in the conversion of prothrombin to thrombin in the bloodstream.
Option C: While calcium is required, Vitamin K is not. Vitamin K's role is in the synthesis of prothrombin in the liver, not its activation in the blood.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Factors involved in the blood coagulation cascade, specifically the conversion of prothrombin to thrombin as background academic context rather than a clinical decision trigger.
Understanding the coagulation cascade is fundamental for interpreting lab tests like Prothrombin Time (PT) and International Normalized Ratio (INR), which assess the extrinsic pathway.
This knowledge is crucial for managing patients on anticoagulant therapy. For example, Warfarin is a Vitamin K antagonist, which works by inhibiting the synthesis of Vitamin K-dependent clotting factors (II, VII, IX, X).
Nurses must monitor for signs of bleeding in patients with liver disease, as the liver synthesizes most clotting factors, or in patients with hypocalcemia (low calcium levels), as calcium is a vital cofactor.

How to Approach the Question

First, identify the core process in the question: the conversion of prothrombin to thrombin.
Recall the three main stages of blood coagulation. This specific conversion is Stage 2.
Consider the requirements for Stage 2. This stage requires prothrombin activator and calcium ions (Factor IV).
Think about how prothrombin activator is formed (Stage 1). The extrinsic pathway, a key route, is initiated by thromboplastin (Factor III).
Evaluate each option based on these facts. Eliminate options containing factors with incorrect roles, such as fibrinogen (product of the next stage) or Vitamin K (involved in synthesis, not activation).
Select the option that correctly identifies the direct cofactor (calcium) and a key initiator of the pathway (thromboplastin).

Concept Tested & Keywords

Concept Tested: Factors involved in the blood coagulation cascade, specifically the conversion of prothrombin to thrombin.
Stem keywords: clotting, prothrombin, thrombin
Lead-in keywords: in the presence of
Negative lead-in flag: false

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