The excessive amount of calcium is regulated by

Options

A. Thyroxine
B. Calcitonin
C. Epinephrine
D. Progesterone.

Answer

To solve the question regarding the regulation of excessive amounts of calcium in the body, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Hormones Involved**: The question provides four options: thyroxine, calcitonin, epinephrine, and progesterone. We need to determine which of these hormones is responsible for regulating calcium levels.

2. **Understand the Role of Calcitonin**: Calcitonin is a hormone produced by the parafollicular cells (C cells) of the thyroid gland. Its primary function is to lower blood calcium levels when they are elevated.

3. **Mechanism of Action of Calcitonin**:
- **Increases Bone Calcium Absorption**: Calcitonin promotes the absorption of calcium into the bones, thereby reducing the amount of calcium in the bloodstream.
- **Decreases Calcium Absorption in Kidneys and Intestines**: It reduces the reabsorption of calcium in the kidneys and intestines, leading to increased calcium excretion in urine.
- **Inhibits Osteoclast Activity**: Calcitonin slows down the activity of osteoclasts, which are the cells responsible for breaking down bone and releasing calcium into the blood.

4. **Eliminate Incorrect Options**:
- **Thyroxine**: While it is produced by the thyroid gland, thyroxine primarily regulates metabolism and does not play a significant role in calcium regulation.
- **Epinephrine**: This hormone is involved in the fight-or-flight response and does not regulate calcium levels.
- **Progesterone**: This hormone is primarily involved in the menstrual cycle and pregnancy, and it does not regulate calcium levels.

5. **Conclusion**: Based on the mechanisms of action and the roles of the hormones listed, the hormone responsible for regulating excessive amounts of calcium is **calcitonin**.

### Final Answer:
The excessive amount of calcium is regulated by **calcitonin**.

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