Calcitonin:
Calcitonin is a hormone that helps regulate calcium and phosphate levels in the blood. It is produced by the thyroid gland, specifically by the parafollicular cells (also known as C cells) located in the thyroid gland.

Role of Calcitonin:
Calcitonin plays a crucial role in maintaining calcium and phosphate homeostasis in the body. It acts primarily on the bones, kidneys, and intestines to regulate the levels of these minerals.

Effects on Bones:
- In the bones, calcitonin inhibits the activity of osteoclasts, which are cells responsible for breaking down bone tissue. By suppressing osteoclast activity, calcitonin helps to prevent excessive bone resorption and maintain bone density.
- This action of calcitonin reduces the release of calcium and phosphate from the bones into the bloodstream, thereby reducing their levels in the blood.

Effects on Kidneys:
- Calcitonin also acts on the kidneys to increase the excretion of calcium and phosphate in urine. This helps to decrease the levels of these minerals in the blood.
- By promoting the elimination of calcium and phosphate, calcitonin helps to maintain their balance and prevent their excessive accumulation in the body.

Effects on Intestines:
- Additionally, calcitonin inhibits the absorption of calcium and phosphate from the intestines. This further helps in regulating their levels in the blood.
- By reducing the absorption of these minerals, calcitonin ensures that only the required amounts are taken up by the body, preventing their excess accumulation.

Overall:
By its actions on the bones, kidneys, and intestines, calcitonin helps to maintain the balance of calcium and phosphate in the blood. It prevents excessive release of these minerals from the bones, promotes their excretion through the kidneys, and inhibits their absorption from the intestines.

Calcitonin works in opposition to another hormone called parathyroid hormone (PTH). While PTH increases blood calcium levels, calcitonin reduces them. Together, PTH and calcitonin maintain the proper balance of calcium and phosphate in the body, ensuring their availability for essential physiological processes while preventing their excess or deficiency.