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: (C)

Calcitonin lowers blood calcium by directly inhibiting osteoclasts, the cells responsible for bone resorption. When osteoclast activity is reduced, less calcium is released from bone into the bloodstream, so serum calcium falls. This is the primary action of calcitonin, making the statement about inhibition of osteoclasts the best description. The other ideas aren’t correct because promoting osteoclasts would raise calcium, not lower it; calcitonin does have an effect on bone cells, so saying it has no effect is false; and its main action isn’t to stimulate osteoblasts to lower calcium, since osteoblast stimulation isn’t the key mechanism by which calcitonin reduces serum calcium.

Calcitonin lowers blood calcium by directly inhibiting osteoclasts, the cells responsible for bone resorption. When osteoclast activity is reduced, less calcium is released from bone into the bloodstream, so serum calcium falls. This is the primary action of calcitonin, making the statement about inhibition of osteoclasts the best description.

The other ideas aren’t correct because promoting osteoclasts would raise calcium, not lower it; calcitonin does have an effect on bone cells, so saying it has no effect is false; and its main action isn’t to stimulate osteoblasts to lower calcium, since osteoblast stimulation isn’t the key mechanism by which calcitonin reduces serum calcium.