Calcitonin

Human calcitonin recptor-Gs complex PDB 7TYO

Calcitonin Bones

Calcitonin is a hormone produced primarily by the thyroid gland's parafollicular cells, also known as C-cells, in humans and many other animals. Its main function is to regulate calcium and phosphate levels in the bloodstream, counteracting the effects of the parathyroid hormone (PTH) which acts to increase blood calcium levels.

Production and Structure

Calcitonin is a 32-amino acid polypeptide hormone. Its secretion is stimulated by high blood calcium levels, and it acts to decrease these levels by inhibiting osteoclast activity in the bones, which in turn reduces the release of calcium from the bone matrix. Additionally, calcitonin reduces the reabsorption of calcium and phosphate from the kidneys, further contributing to a decrease in blood calcium levels.

Functions

The primary role of calcitonin is the regulation of calcium and phosphate metabolism. By inhibiting osteoclast activity, it plays a crucial role in bone remodeling and helps prevent excessive bone resorption, contributing to the maintenance of bone density and strength. In the kidneys, its action reduces calcium and phosphate reabsorption, leading to their increased excretion in the urine.

Clinical Significance

1. 1. 1. Osteoporosis Treatment###

Calcitonin has been used in the treatment of osteoporosis, a condition characterized by decreased bone density and increased risk of fractures. It is particularly useful in patients who cannot tolerate other osteoporosis medications. However, its use has declined due to the availability of more effective treatments.

1. 1. 1. Paget's Disease###

It is also used in the management of Paget's disease of bone, a chronic disorder that can result in enlarged and misshapen bones. Calcitonin can help regulate bone formation and resorption in this condition, alleviating symptoms and preventing complications.

1. 1. 1. Hypercalcemia###

Calcitonin can be used to treat hypercalcemia, or high blood calcium levels, especially when they are caused by cancer. Its rapid action in lowering blood calcium levels makes it useful in acute cases.

Pharmacology

Calcitonin is available as a pharmaceutical preparation, derived either from salmon or produced synthetically. Salmon calcitonin is more potent than human calcitonin and has a longer half-life, making it more effective for therapeutic use. It can be administered via injection or nasal spray.

Side Effects

The use of calcitonin can be associated with side effects such as nausea, flushing, and an allergic reaction at the injection site. Long-term use, especially of the nasal spray, has been linked to a slightly increased risk of cancer, although the evidence is not conclusive.

Conclusion

Calcitonin plays a vital role in calcium and phosphate metabolism, with significant implications for bone health. While its therapeutic use has been overshadowed by newer treatments for osteoporosis and other bone diseases, it remains an important tool in the management of hypercalcemia and Paget's disease.