What effect does calcitonin have on blood calcium levels?

Calcitonin is a hormone produced by the parafollicular cells (C cells) of the thyroid gland, and its primary role is to help regulate calcium levels in the blood. When blood calcium levels are elevated, calcitonin is released in response. This hormone acts to decrease blood calcium levels through several mechanisms.

Firstly, calcitonin inhibits osteoclast activity in the bones, which are the cells responsible for breaking down bone tissue and releasing calcium into the bloodstream. By inhibiting osteoclasts, calcitonin reduces the amount of calcium being released from the bone, thus promoting a decrease in blood calcium levels.

Secondly, calcitonin also promotes renal excretion of calcium. It increases the amount of calcium excreted by the kidneys, which further contributes to lowering blood calcium levels.

By combining these actions — suppressing the release of calcium from bone and promoting its excretion by the kidneys — calcitonin effectively reduces overall blood calcium concentrations, confirming that its primary effect is to decrease blood calcium levels.