Question

Arrange the following steps involved in extrinsic pathway of blood clotting in correct sequence:
(A) Formation of Prothrombinase
(B) Activation of enzyme Prothrombinase
(C) Tissue factor (TF) or Thromboplastin leaks in blood vessels
(D) Ca$^{2+}$ and TF activates clotting factor X
(E) Clotting factor X combines with clotting factor V in presence of Ca$^{2+}$

• A. (B), (A), (E), (D), (C)
• B. (C), (D), (E), (A), (B)
• C. (A), (B), (C), (D), (E)
• D. (B), (E), (A), (D), (C)
• E.

Hint:

Extrinsic pathway starts with Tissue Factor (TF). Always remember the sequence: TF + Ca$^{2+}$ → Factor X activation → Factor V joining → Prothrombinase formation → Activation of Prothrombinase.

Answer 1

The Correct Option is B

Step 1: Extrinsic Pathway Initiation.
The extrinsic pathway commences with the leakage of tissue factor (TF), or thromboplastin, into the bloodstream from damaged tissues. Therefore, the first step corresponds to (C). Step 2: Clotting Factor X Activation.
In the presence of calcium ions (Ca$^{2+}$) and tissue factor, clotting factor X undergoes activation. Consequently, the second step is denoted by (D). Step 3: Active Complex Formation.
Activated factor X, in conjunction with factor V and Ca$^{2+}$, forms the Prothrombinase complex. Thus, the third step is represented by (E). Step 4: Prothrombinase Generation.
This complex facilitates the actual synthesis of the Prothrombinase enzyme. Accordingly, the fourth step is designated as (A). Step 5: Prothrombinase Activation.
Finally, Prothrombinase becomes activated and catalyzes the conversion of Prothrombin to Thrombin. Hence, the fifth step is identified as (B). Step 6: Summary.
The correct sequence of events is (C) → (D) → (E) → (A) → (B).