Natural anticoagulant is

Options

A. Serotonin
B. Digitonin
C. Heparin
D. Erythromtcin.

Answer

**Step-by-Step Solution:**

1. **Understanding Anticoagulants**: Anticoagulants are substances that prevent blood from clotting. They play a crucial role in maintaining normal blood flow and preventing conditions such as thrombosis.

2. **Identifying Natural Anticoagulants**: There are several natural anticoagulants present in the body. Some of the most notable ones include:
- **Protein C**: This protein, when activated, helps to inactivate factors that promote clotting.
- **Protein S**: This acts as a cofactor to Protein C, enhancing its anticoagulant effects.
- **Antithrombin**: This protein inhibits thrombin and other clotting factors, thereby preventing excessive clot formation.
- **Heparin**: A well-known natural anticoagulant that enhances the activity of antithrombin.

3. **Mechanism of Action**: The primary way these anticoagulants function is by inactivating thrombin, a key enzyme in the clotting process. By inactivating thrombin, they prevent the conversion of fibrinogen to fibrin, which is essential for blood clot formation.

4. **Conclusion**: Among the options provided, heparin is recognized as a natural anticoagulant. Therefore, the correct answer to the question "Natural anticoagulant is" would be heparin.

**Final Answer**: Heparin

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