Flex Your Knowledge: Ace the Muscular and Skeletal System Test 2026!

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Summarize key hormones involved in calcium homeostasis and their actions on bone and kidney.

Parathyroid hormone decreases blood calcium by promoting calcium excretion; calcitonin lowers; vitamin D reduces intestinal absorption; kidneys inactivate vitamin D.

Parathyroid hormone increases blood calcium by promoting bone resorption and renal reabsorption; calcitonin lowers; vitamin D enhances intestinal absorption; kidneys convert vitamin D to its active form.

Calcium homeostasis is controlled by hormones that coordinate bone remodeling, kidney handling, and intestinal absorption. Parathyroid hormone responds to low blood calcium by raising Ca2+ levels: it promotes bone resorption to release calcium, increases renal calcium reabsorption, and stimulates the kidney to activate vitamin D, which then boosts intestinal calcium uptake. Calcitonin works in the opposite direction, helping to lower blood calcium by inhibiting osteoclast activity and reducing bone resorption. Vitamin D, once activated in the kidney, increases intestinal calcium absorption and supports bone mineralization, with the kidney also converting vitamin D to its active form to enable these effects. This combination of actions matches the described roles, making it the best summary of how these hormones regulate calcium on bone and kidney.

Calcitonin increases bone resorption; PTH reduces calcium reabsorption.

Vitamin D has no role in calcium absorption.

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