Antagonist pair off hormone which regulate `Ca^(+2)` in blood are

Answer

To answer the question about the antagonist pair of hormones that regulate calcium levels in the blood, we can follow these steps:

### Step-by-Step Solution:

1. **Understand the Concept of Antagonistic Hormones**:
- Antagonistic hormones are pairs of hormones that have opposite effects on a particular physiological process. In this case, we are looking for hormones that regulate calcium levels in the blood.

2. **Identify the Hormones Involved in Calcium Regulation**:
- The two primary hormones that regulate calcium levels in the blood are **calcitonin** and **parathyroid hormone (PTH)**.

3. **Function of Calcitonin**:
- Calcitonin is produced by the thyroid gland and functions to **decrease blood calcium levels**. It does this by inhibiting the activity of osteoclasts (cells that break down bone) and promoting the deposition of calcium in the bones.

4. **Function of Parathyroid Hormone (PTH)**:
- Parathyroid hormone is produced by the parathyroid glands and has the opposite effect of calcitonin. It functions to **increase blood calcium levels** by stimulating osteoclast activity, promoting calcium reabsorption in the kidneys, and enhancing intestinal absorption of calcium.

5. **Conclusion**:
- Therefore, the antagonist pair of hormones that regulate calcium in the blood are **calcitonin** and **parathyroid hormone (PTH)**.

### Final Answer:
The antagonist pair of hormones that regulate calcium in the blood are **calcitonin** and **parathyroid hormone (PTH)**.

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