Blood calcium level is a resultant of how much dietary calcium is absorbed ,Hoe much calcium is lost in urine,how much bone dissoves releasing calcium into the blood and how much calcium from blood enters tissues.A number of facctors play an important role in these processes.Mask the one which has no role.

Options

A. Vitamin D
B. Parathyroid hormone
C. Thyrocalcitonin
D. Thymosin

Answer

To solve the question regarding which factor does not play a role in blood calcium level regulation, we will analyze each of the given options in relation to calcium metabolism.

### Step-by-Step Solution:

1. **Understanding Blood Calcium Levels**: Blood calcium levels are influenced by several factors including dietary absorption, urinary loss, bone dissolution, and tissue uptake.

2. **Identifying the Factors**: The options provided are:
- Vitamin D
- Parathyroid hormone
- Thyrocalcitonin (Calcitonin)
- Thymocin

3. **Role of Vitamin D**: Vitamin D is essential for the absorption of calcium from the intestines. It helps increase the amount of calcium that is absorbed from the food we eat, thus playing a crucial role in maintaining blood calcium levels.

4. **Role of Parathyroid Hormone (PTH)**: Parathyroid hormone is secreted by the parathyroid glands and increases blood calcium levels by promoting the release of calcium from bones and increasing calcium reabsorption in the kidneys. Therefore, it is also involved in calcium metabolism.

5. **Role of Thyrocalcitonin (Calcitonin)**: Calcitonin is produced by the thyroid gland and helps lower blood calcium levels by promoting the deposition of calcium in bones and reducing calcium reabsorption in the kidneys. It is involved in calcium regulation.

6. **Role of Thymocin**: Thymocin is a hormone produced by the thymus gland and is primarily involved in the immune response by aiding in the development of T cells. It does not have any role in calcium metabolism.

7. **Conclusion**: Based on the analysis, the factor that does not play a role in calcium metabolism is **Thymocin**.

### Final Answer:
**Thymocin** is the factor that has no role in blood calcium level regulation.