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Parathyroid Hormone and Calcitonin: Opposing Calcium Control

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Parathyroid hormone raises blood calcium by stimulating bone breakdown and kidney and intestinal absorption; calcitonin lowers it by inhibiting bone breakdown, opposing PTH through feedback on each trigger.

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Falling blood calcium triggers PTH release; rising blood calcium triggers calcitonin release.

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Calcitonin's role in healthy adults remains poorly defined compared with PTH's, despite a clearer role in children and pregnancy.