Kalsitoniinin

Kalsitoniinin is a thyroid hormone that plays a role in calcium and phosphorus metabolism. It is a polypeptide hormone produced by the parafollicular cells, also known as C cells, of the thyroid gland in mammals. In non-mammalian vertebrates, it is synthesized in the ultimobranchial glands.

The primary function of kalsitoniinin is to lower blood calcium levels when they become too high. It achieves this through several mechanisms. Kalsitoniinin inhibits the activity of osteoclasts, which are cells responsible for bone resorption, thereby reducing the release of calcium from bone into the bloodstream. It also promotes the excretion of calcium and phosphate by the kidneys. Additionally, it can inhibit the absorption of calcium from the intestines.

The secretion of kalsitoniinin is primarily stimulated by elevated levels of calcium in the blood. This creates a negative feedback loop where high calcium triggers the release of kalsitoniinin, which then works to bring calcium levels back down.

While kalsitoniinin has a clear role in calcium homeostasis, its importance in humans is generally considered to be less significant than that of parathyroid hormone (PTH), which raises blood calcium levels. In certain pathological conditions, such as medullary thyroid carcinoma, excessive amounts of kalsitoniinin can be produced, leading to hypocalcemia. Therapeutically, synthetic kalsitoniinin has been used to treat conditions like Paget's disease of bone, hypercalcemia, and osteoporosis, although its use in osteoporosis has largely been replaced by other medications.