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How does calcitonin lower calcium levels in the blood?

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Hormone Many important physiological functions of vertebrates are controlled by steroid hormones.

Calcitonin is a protein hormone produced by parafollicular cells (C cells) in the thyroid gland. It functions to lower elevated levels of calcium and phosphorus in the blood through two primary mechanisms:12

Inhibition of Bone Resorption: Calcitonin inhibits the activity of osteoclasts, the cells responsible for breaking down bone tissue. By preventing this breakdown, it stops the release of calcium from the bones into the bloodstream.12
Increased Excretion: The hormone inhibits the reabsorption of calcium by the cells of the kidney, which promotes the excretion of calcium through the urine.2

These actions effectively counter the effects of parathyroid hormone, which works to increase serum calcium concentrations. Notably, the effects of calcitonin are relatively short-lived, typically waning within a few days, which limits its utility as a long-term treatment for chronic hypercalcemia.21