State: Functions of parathyroid gland.

Answer

### Step-by-Step Solution:

1. **Definition of Parathyroid Gland**:
The parathyroid glands are small endocrine glands located on the posterior surface of the thyroid gland. There are typically four parathyroid glands, two on each lobe of the thyroid.

2. **Secretion of Parathyroid Hormone (PTH)**:
The primary function of the parathyroid glands is to secrete a peptide hormone known as parathyroid hormone (PTH).

3. **Regulation of Calcium Levels**:
PTH plays a crucial role in regulating calcium levels in the blood. It increases the concentration of calcium ions (Ca²⁺) in the bloodstream.

4. **Bone Resorption**:
One of the ways PTH increases blood calcium levels is by stimulating bone resorption. This process involves the dissolution of bone tissue, which releases calcium into the bloodstream.

5. **Reabsorption of Calcium**:
PTH also promotes the reabsorption of calcium in the kidneys, reducing the amount of calcium excreted in urine.

6. **Increased Calcium Absorption from Food**:
Additionally, PTH enhances the absorption of calcium from the food we consume in the intestines.

7. **Classification as Hypercalcemic Hormone**:
Due to its role in increasing calcium levels in the blood, PTH is classified as a hypercalcemic hormone.

8. **Interaction with Other Hormones**:
PTH works alongside another hormone called calcitonin (secreted by the thyroid gland) to maintain calcium balance in the body.

### Summary of Functions of Parathyroid Gland:
- Secretion of parathyroid hormone (PTH).
- Regulation of blood calcium levels by increasing Ca²⁺ concentration.
- Stimulation of bone resorption to release calcium.
- Promotion of calcium reabsorption in the kidneys.
- Enhancement of calcium absorption from digested food.
- Classification as a hypercalcemic hormone.