Under what condition is calcitonin released by the body?

Calcitonin is a hormone produced by the parafollicular cells (C cells) of the thyroid gland, and its primary role is to help regulate calcium levels in the body. The release of calcitonin is triggered when serum calcium levels rise. Its function is to lower blood calcium levels when they become elevated, primarily by inhibiting osteoclast activity in the bones—those cells that break down bone tissue and release calcium into the bloodstream. Additionally, calcitonin reduces calcium reabsorption in the kidneys, promoting its excretion.

In the context of maintaining homeostasis, this mechanism is vital for preventing hypercalcemia, which, if unchecked, could result in negative health outcomes such as kidney stones, bone weakness, and interference with nerve function. Therefore, the presence of elevated serum calcium levels directly stimulates the secretion of calcitonin, making it a crucial hormone in calcium metabolism.