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: Initiation of extrinsic pathway.
The extrinsic pathway begins when tissue factor (TF), also called thromboplastin, leaks into the blood from damaged tissues.
So the first step is (C).
Step 2: Activation of clotting factor X.
In the presence of calcium ions (Ca$^{2+}$) and tissue factor, clotting factor X is activated.
So the second step is (D).
Step 3: Formation of active complex.
Activated factor X then combines with factor V in the presence of Ca$^{2+}$, forming Prothrombinase complex.
So the third step is (E).
Step 4: Formation of Prothrombinase.
This complex leads to the actual formation of Prothrombinase enzyme.
So the fourth step is (A).
Step 5: Activation of Prothrombinase.
Finally, Prothrombinase is activated and it converts Prothrombin into Thrombin.
So the fifth step is (B).
Step 6: Conclusion.
The correct order is (C) → (D) → (E) → (A) → (B).