What is the main function of calcitonin in the body?

Calcitonin primarily functions to prevent hypercalcemia, which refers to elevated levels of calcium in the blood. It is a hormone secreted by the parafollicular cells (or C cells) of the thyroid gland in response to high blood calcium levels. When released, calcitonin acts to lower blood calcium levels by inhibiting osteoclast activity in the bones, which are responsible for bone resorption and the release of calcium into the bloodstream. Additionally, it enhances the excretion of calcium through the kidneys.

By promoting these actions, calcitonin plays a crucial role in maintaining calcium homeostasis in the body, ensuring that calcium levels remain within a narrow and healthy range. This is essential for various physiological processes, including muscle contraction, nerve function, and blood clotting. Therefore, the main function of calcitonin, as represented by the correct choice, is to prevent hypercalcemia.