Function of thyrocalcitonin :

Options

A. To reduce the calcium level in blood
B. To increase the calcium level in blood
C. Oppose the action of thyroxine
D. Maturation of gonads

Answer

### Step-by-Step Solution:

1. **Identify the Hormone**: The hormone in question is thyrocalcitonin, also known as calcitonin.

2. **Source of Production**: Calcitonin is secreted by parafollicular cells (also called C-cells) located in the thyroid gland.

3. **Nature of the Hormone**: Calcitonin is a proteinaceous hormone, meaning it is made up of proteins.

4. **Primary Function**: The main function of calcitonin is to lower the calcium levels in the blood. It does this by promoting the deposition of calcium into the bone matrix.

5. **Mechanism of Action**: Calcitonin works by inhibiting osteoclast activity (cells that break down bone) and stimulating osteoblast activity (cells that build bone), leading to increased calcium storage in bones and decreased calcium levels in the bloodstream.

6. **Comparison with Other Hormones**: To maintain calcium homeostasis, calcitonin works in opposition to parathyroid hormone (PTH), which increases blood calcium levels. While calcitonin decreases calcium levels, PTH increases them.

7. **Elimination of Incorrect Options**:
- Option B (to increase calcium level in blood) is incorrect because calcitonin reduces calcium levels.
- Option C (oppose the action of thyroxine) is incorrect as calcitonin is not involved in the regulation of thyroxine.
- Option D (maturation of gonads) is incorrect because gonadal maturation is regulated by gonadotropins, not calcitonin.

8. **Conclusion**: The correct answer is that the function of thyrocalcitonin is to reduce the calcium level in the blood.

### Final Answer:
The function of thyrocalcitonin is to reduce the calcium level in the blood.

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