Heparin inactivates all of the following clotting factors except –
**Core Concept**
Heparin is an anticoagulant that works by activating **antithrombin III**, which then inactivates several **clotting factors**. This mechanism is crucial for preventing thrombosis. Heparin's action is primarily through the enhancement of antithrombin's ability to inhibit these factors.
**Why the Correct Answer is Right**
Since the correct answer choices are not provided, let's discuss the general principle: Heparin, through antithrombin, primarily inactivates factors IIa (thrombin), Xa, IXa, XIa, and XIIa. However, it does not directly inactivate all clotting factors, suggesting there's an exception among the typical factors affected by heparin's anticoagulant activity.
**Why Each Wrong Option is Incorrect**
**Option A:** Without specific details, we generally know that heparin inactivates several key clotting factors, so if A represents one of these (e.g., factor IIa), it would be incorrect because heparin does inactivate it.
**Option B:** Similarly, if B represents another factor typically inactivated by heparin (like factor Xa), it would be an incorrect choice for the same reason.
**Option C:** If C is a factor not usually associated with heparin's mechanism (like factor VII), this might seem plausible, but without specifics, we cannot definitively say why it's incorrect based solely on the question.
**Option D:** Assuming D represents a factor heparin does inactivate, it would be an incorrect choice.
**Clinical Pearl / High-Yield Fact**
A key point to remember is that heparin's primary mechanism involves the activation of **antithrombin III**, which then inhibits several clotting factors, highlighting the importance of antithrombin in heparin's anticoagulant effect.
**Correct Answer:** Correct Answer: D. Factor VIII