Kaltsitoniini

Kaltsitoniini is a polypeptide hormone produced by the parafollicular cells (also known as C-cells) of the thyroid gland in mammals. It plays a role in calcium and phosphate homeostasis. Its primary function is to lower blood calcium levels.

When blood calcium rises, calcitonin is released. It acts on bone by inhibiting osteoclast activity, thereby reducing the rate at which calcium is released from bone. It also affects the kidneys, increasing the excretion of calcium and phosphate in the urine. While its role in healthy humans is considered less significant than that of parathyroid hormone in regulating minute-to-minute calcium levels, it can be important during periods of high calcium turnover, such as pregnancy and lactation.

Calcitonin also exists in other vertebrates, where it is produced by ultimobranchial glands. The structure and potency can vary between species. Synthetic calcitonin, often derived from salmon calcitonin due to its higher potency and longer duration of action in humans compared to human calcitonin, is used therapeutically. It is administered to treat conditions such as Paget's disease of bone, hypercalcemia, and osteoporosis, where it helps to reduce bone resorption and alleviate pain.