Zona pellucida is secreted by

Options

A. Primary oocyte
B. Secondary ooctye
C. Corona radiata
D. Ootid

Answer

### Step-by-Step Solution:

1. **Understanding Zona Pellucida**:
- The zona pellucida is a glycoprotein layer that surrounds the oocyte (egg) and plays a crucial role in fertilization and protection of the egg.

2. **Function of Zona Pellucida**:
- It supports communication between the oocyte and the surrounding follicle cells during oogenesis.
- It regulates interactions between the ovulated egg and sperm during fertilization.

3. **Formation of Zona Pellucida**:
- The zona pellucida is formed by the secretion of substances from the oocyte itself, particularly the secondary oocyte.
- It consists of a thick matrix that includes glycoproteins.

4. **Components of Zona Pellucida**:
- In humans, the zona pellucida is made up of four types of glycoproteins: ZP1, ZP2, ZP3, and ZP4, each playing different roles in the fertilization process.

5. **Identifying the Source of Secretion**:
- The zona pellucida is specifically secreted by the secondary oocyte, which is the mature form of the oocyte that is ready for fertilization.
- Other options like primary oocyte, corona radiata, and ootid do not secrete the zona pellucida.

6. **Conclusion**:
- Therefore, the correct answer to the question "Zona pellucida is secreted by" is the **secondary oocyte**.