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14.10: Calcitonin (Thyrocalcitonin)

Last updated

Oct 19, 2023
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- 14.9: Thyroid Hormones (T3 and T4)
- 14.11: Parathormone

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Sources and Control of Secretion

Though most thyroid gland cells secrete thyroid hormones, others secrete calcitonin (thyrocalcitonin). Calcitonin secretion is controlled by blood calcium levels, using a simple negative feedback mechanism that does not involve the hypothalamus or pituitary gland but instead uses substrate control. High blood levels of calcium stimulate calcitonin secretion, which causes blood calcium levels to decline by stimulating removal of calcium from the blood. The resulting lower blood calcium levels then reduce calcitonin secretion and allow parathormone to raise blood calcium levels. When blood calcium rises, calcitonin secretion increases again. As a result, homeostasis of blood calcium is maintained.

Effects

Calcitonin decreases blood calcium by stimulating osteoblasts to incorporate blood calcium into bone matrix, inhibiting osteoclasts from removing calcium from bone matrix, and allowing the kidneys to release more calcium in the urine.

Age Changes

Calcitonin levels may decrease with age, increasing the risk of osteoporosis in some individuals. Furthermore, the possible decrease in the effectiveness of calcitonin which may be caused by decreases in estrogen, may play an additional role in the development of osteoporosis in women (see Sex Hormones in Women, below).

Sources and Control of Secretion

Effects

Age Changes

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