kalsítónín

Kalsítónín is a hormone produced by the parafollicular cells, also known as C cells, of the thyroid gland in mammals. In birds, reptiles, amphibians, and fish, it is produced by the ultimobranchial bodies. The primary role of calcitonin is to regulate calcium and phosphate levels in the blood. It acts antagonistically to parathyroid hormone (PTH).

When blood calcium levels rise, calcitonin is secreted, which inhibits osteoclast activity. Osteoclasts are cells responsible for bone resorption, so by inhibiting them, calcitonin reduces the release of calcium from bone into the bloodstream. It also promotes calcium excretion by the kidneys, further lowering blood calcium levels. In some species, calcitonin can also increase bone formation by osteoblasts.

The clinical significance of calcitonin is related to its role in bone metabolism. Synthetic calcitonin is used therapeutically to treat conditions such as osteoporosis, Paget's disease of bone, and hypercalcemia. It can help reduce bone loss and alleviate pain associated with these conditions. However, its use in osteoporosis treatment has become less common with the advent of other more effective therapies. Calcitonin levels can be monitored as a tumor marker for medullary thyroid carcinoma, a type of thyroid cancer that arises from the C cells.