Calcium level is not regulated by

Options

A. Vitamin D
B. Thyroxine
C. Calcitonin
D. Collip's hormone

Answer

To determine which option does not regulate calcium levels, let's analyze each option step by step.

### Step-by-Step Solution:

1. **Understanding Calcium Regulation**: Calcium levels in the body are regulated by various hormones, which include vitamin D, calcitonin, and parathyroid hormone (often referred to as collipse hormone).

2. **Option A: Vitamin D**:
- Vitamin D plays a crucial role in calcium metabolism. It facilitates the absorption of calcium from the small intestine into the bloodstream.
- Therefore, vitamin D does regulate calcium levels.

3. **Option B: Thyroxin**:
- Thyroxin is a hormone produced by the thyroid gland. Its primary functions include regulating metabolism and body temperature.
- Thyroxin does not have a direct role in regulating calcium levels in the blood.
- Thus, thyroxin is a candidate for the answer.

4. **Option C: Calcitonin**:
- Calcitonin is a hormone secreted by the thyroid gland that helps lower blood calcium levels by inhibiting osteoclast activity (cells that break down bone).
- Therefore, calcitonin does regulate calcium levels.

5. **Option D: Collipse Hormone (Parathyroid Hormone)**:
- Collipse hormone, also known as parathyroid hormone (PTH), increases blood calcium levels by stimulating osteoclasts, promoting calcium reabsorption in the kidneys, and enhancing intestinal absorption of calcium.
- Hence, this hormone also regulates calcium levels.

6. **Conclusion**:
- After analyzing all the options, we find that the only hormone that does not regulate calcium levels is **thyroxin**.
- Therefore, the correct answer is **Option B: Thyroxin**.

### Final Answer:
**Option B: Thyroxin**