Which substance initiate clotting of blood ?

Options

A. Prothrombin
B. Antithrombin
C. Prothrombinase
D. Thromboplastin

Answer

**Step-by-Step Solution:**

1. **Understanding Blood Clotting**: Blood clotting, also known as coagulation, is a complex process that prevents excessive bleeding when a blood vessel is injured. It involves a series of biochemical reactions that lead to the formation of a blood clot.

2. **Identifying Key Substances in Clotting**: There are several key substances involved in the clotting process, including various proteins and enzymes. Some of these include prothrombin, thrombin, antithrombin, and thromboplastin.

3. **Evaluating Prothrombin**: Prothrombin is a protein produced in the liver that is essential for blood clotting. However, it is not the substance that initiates the clotting process; instead, it is converted into thrombin during the clotting cascade.

4. **Evaluating Antithrombin**: Antithrombin is a plasma protein that regulates blood coagulation. It acts to inhibit clotting factors and prevent excessive clotting, but it does not initiate the clotting process.

5. **Revisiting Prothrombin**: The mention of prothrombin again in the context of its role in the coagulation cascade is a reiteration that it is not the initiator but rather a participant in the process.

6. **Identifying Thromboplastin**: Thromboplastin, also known as tissue factor, is the substance that initiates the clotting process. It is released from damaged tissues and interacts with other clotting factors to start the coagulation cascade.

7. **Conclusion**: Based on the evaluation of the options, the substance that initiates blood clotting is **thromboplastin**.

**Final Answer**: Thromboplastin initiates the clotting of blood.

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