Which of the following clotting factor is not involved in intrinsic pathway?
**Core Concept**
The intrinsic pathway of blood coagulation involves a series of enzyme-catalyzed reactions that ultimately lead to the formation of a blood clot. This pathway is activated by trauma to a blood vessel and is characterized by the involvement of clotting factors that are not dependent on tissue factor.
**Why the Correct Answer is Right**
The correct answer is not directly provided, but based on the options typically available for this question, we can infer that the intrinsic pathway involves factors such as Factor XII, Factor XI, Factor IX, and Factor VIII. These factors work together in a cascade to activate Factor X, which then converts prothrombin to thrombin, leading to clot formation.
**Why Each Wrong Option is Incorrect**
* **Option A:** Factor VII is actually involved in the extrinsic pathway of blood coagulation, not the intrinsic pathway. It is activated by tissue factor and plays a crucial role in initiating the coagulation cascade.
* **Option B:** Factor X is a key component of the intrinsic pathway and is activated by the Factor IXa-Factor VIIIa complex. It then goes on to activate prothrombin to thrombin.
* **Option C:** Factor V is also involved in the intrinsic pathway and serves as a cofactor for the Factor Xa-thrombin complex.
* **Option D:** Factor II (prothrombin) is not a clotting factor that is involved in the intrinsic pathway, but rather is the substrate that is converted to thrombin by the Factor Xa-thrombin complex.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the intrinsic pathway is activated by trauma to a blood vessel, whereas the extrinsic pathway is activated by tissue factor. Understanding the differences between these two pathways is crucial for managing bleeding disorders and preventing thrombosis.
**Correct Answer:** A. Factor VII