Calcitonins

Calcitonins are a group of peptide hormones produced primarily by the parafollicular cells, also known as C-cells, of the thyroid gland in mammals. In non-mammalian vertebrates, calcitonin is synthesized by ultimobranchial bodies. The primary role of calcitonin is to regulate calcium and phosphate levels in the blood, acting in opposition to parathyroid hormone.

When blood calcium levels rise, calcitonin secretion increases. Its main actions include inhibiting the activity of osteoclasts, the cells responsible for bone resorption, thereby decreasing the release of calcium from bones into the bloodstream. It also promotes the excretion of calcium and phosphate by the kidneys. These effects contribute to lowering both serum calcium and phosphate concentrations.

While its role in calcium homeostasis is well-established, especially in fish and amphibians where it plays a significant part, its importance in adult humans is considered less critical compared to parathyroid hormone. However, calcitonin does have therapeutic applications. Synthetic calcitonin is used to treat conditions like Paget's disease of bone, hypercalcemia (high blood calcium levels), and osteoporosis, where it can help reduce bone loss. Calcitonin also has analgesic properties and can be used to manage pain associated with bone metastases.