Thrombocytes secrete  

Options

A. fibrinogen
B. prothrombin
C. thromboplastin
D. fibrin

Answer

To answer the question "Thrombocytes secrete," we need to analyze the options provided and understand the role of thrombocytes (platelets) in the blood clotting process.

### Step-by-Step Solution:

1. **Understanding Thrombocytes**:
- Thrombocytes, also known as platelets, are small cell fragments derived from larger cells called megakaryocytes found in the bone marrow. Their primary function is to aid in blood clotting and wound healing.

2. **Identifying the Options**:
- The options given are:
- Fibrinogen
- Prothrombin
- Thromboplastin
- Fibrin

3. **Evaluating Each Option**:
- **Fibrinogen**: This is a soluble protein produced by the liver that plays a crucial role in blood clotting. However, it is not secreted by thrombocytes.
- **Prothrombin**: This is another protein produced by the liver that is essential for blood coagulation. Like fibrinogen, it is not secreted by platelets.
- **Fibrin**: This is a protein that forms a mesh-like structure during clot formation, derived from fibrinogen through the action of thrombin. Fibrin itself is not secreted by platelets.
- **Thromboplastin**: This is a mixture of phospholipids and tissue factor released by platelets that helps in converting prothrombin into thrombin, facilitating the clotting process.

4. **Conclusion**:
- The correct answer is **Thromboplastin**. Thrombocytes secrete thromboplastin, which is essential for the coagulation cascade that leads to the formation of a blood clot.

### Final Answer:
Thrombocytes secrete **thromboplastin**.