What role does Calcitonin play in bone metabolism?

• A. Increases blood calcium levels
• B. Inhibits osteoclasts and stimulates osteoblasts
• C. Decreases estrogen levels
• D. Promotes osteoclast activity

Answer: (B)

Calcitonin is a hormone produced primarily by the thyroid gland that plays a significant role in regulating bone metabolism. Its primary function is to help lower blood calcium levels when they rise above normal. It achieves this by inhibiting the activity of osteoclasts, which are the cells responsible for bone resorption. When osteoclast activity is reduced, the breakdown of bone is decreased, leading to less calcium being released into the bloodstream. Additionally, calcitonin indirectly supports bone formation by stimulating osteoblasts, the cells that promote bone building and mineralization.

By combining the inhibition of osteoclasts and the stimulation of osteoblasts, calcitonin helps maintain bone density and strength. This dual action is crucial, especially in conditions characterized by excessive bone loss, such as osteoporosis. Thus, the correct answer highlights calcitonin's role in balancing bone metabolism by affecting both resorption and formation processes.