Which statement about calcitonin's effect on calcium is accurate?

Which statement about calcitonin's effect on calcium is accurate?

• A. It raises blood calcium by promoting osteoclasts
• B. It has no effect on bone cells
• C. It lowers blood calcium by inhibiting osteoclasts
• D. It lowers blood calcium by stimulating osteoblasts

Answer: (D)

Calcitonin lowers blood calcium primarily by stopping bone breakdown. Osteoclasts are the cells that resorb bone and release calcium into the bloodstream. When calcitonin acts, it suppresses osteoclast activity, so bone resorption decreases and less calcium is released into the blood. The net result is a fall in circulating calcium. While osteoblasts build bone and can contribute to calcium sequestration in bone, calcitonin’s direct and dominant action is to inhibit osteoclasts rather than to stimulate osteoblasts.

Calcitonin lowers blood calcium primarily by stopping bone breakdown. Osteoclasts are the cells that resorb bone and release calcium into the bloodstream. When calcitonin acts, it suppresses osteoclast activity, so bone resorption decreases and less calcium is released into the blood. The net result is a fall in circulating calcium. While osteoblasts build bone and can contribute to calcium sequestration in bone, calcitonin’s direct and dominant action is to inhibit osteoclasts rather than to stimulate osteoblasts.