Fibrin is formed from fibrinogen due to activity of

Options

A. Prothrombin
B. Active thrombin
C. Heparin
D. Antiprothrombin

Answer

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about the formation of fibrin from fibrinogen and which component is responsible for this process.

2. **Identifying Key Components**:
- **Fibrinogen**: A soluble plasma protein that is converted into fibrin.
- **Fibrin**: An insoluble protein that forms the meshwork of a blood clot.
- **Thrombin**: An enzyme that plays a crucial role in the conversion of fibrinogen to fibrin.

3. **Role of Thrombin**:
- When an injury occurs, platelets aggregate at the site of the injury.
- These activated platelets release a substance called thromboplastin.

4. **Conversion Process**:
- Thromboplastin catalyzes the conversion of prothrombin (an inactive precursor) into active thrombin.
- Active thrombin is a proteolytic enzyme that specifically cleaves fibrinogen.

5. **Fibrin Formation**:
- Once fibrinogen is cleaved by thrombin, it is transformed into fibrin filaments.
- These filaments then aggregate to form an insoluble network that constitutes the blood clot.

6. **Conclusion**:
- The correct answer to the question is **active thrombin**, as it is the enzyme responsible for converting fibrinogen into fibrin.

### Final Answer:
Fibrin is formed from fibrinogen due to the activity of **active thrombin**.

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