What is the primary function of calcitonin?

Calcitonin is primarily involved in the regulation of calcium levels in the blood. It is a peptide hormone produced by the parafollicular cells (C cells) of the thyroid gland and plays a crucial role in maintaining calcium homeostasis. The primary function of calcitonin is to lower blood calcium levels by inhibiting osteoclast activity in the bones, which are the cells responsible for bone resorption. By decreasing the activity of these cells, calcitonin helps to reduce the release of calcium from bones into the bloodstream.

Additionally, calcitonin promotes the excretion of calcium by the kidneys, further contributing to a reduction in blood calcium levels. This action is essential, particularly after meals when calcium levels may rise due to dietary intake. Thus, the correct choice emphasizes its role as a hormone that lowers blood calcium levels, distinguishing it from other hormones or peptides with different functions regarding calcium and glucose metabolism.