Mast cells secrete

Options

A. haemoglobin
B. heparin
C. myoglobin
D. histamine

Answer

**Step-by-Step Solution:**

1. **Identify the Question**: The question asks what mast cells secrete.

2. **Understand Mast Cells**: Mast cells are a type of white blood cell that play a crucial role in the immune system. They are involved in allergic reactions and help defend the body against pathogens.

3. **Evaluate the Options**: The options provided are:
- Hemoglobin
- Heparin
- Myoglobin
- Histamine

4. **Analyze Each Option**:
- **Hemoglobin**: This is a protein found in red blood cells that carries oxygen. It is not secreted by mast cells.
- **Heparin**: This is an anticoagulant that prevents blood clotting and is secreted by basophils, not mast cells.
- **Myoglobin**: This is a protein that carries oxygen in muscle tissues and is released from damaged muscles. It is not secreted by mast cells.
- **Histamine**: This is a compound involved in local immune responses and is indeed secreted by mast cells. It plays a significant role in inflammatory responses and allergic reactions.

5. **Conclusion**: The correct answer is **Histamine**, as it is the substance that mast cells secrete.

**Final Answer**: Mast cells secrete **Histamine**.

---