Final answer:
Calcitonin is the hormone produced by the parafollicular cells, or C cells, of the thyroid gland which lowers blood calcium levels by enhancing the deposition of calcium into bones and reducing osteoclast activity.
Step-by-step explanation:
The hormone synthesized by the parafollicular cells of the thyroid gland that is secreted when serum concentration of calcium ions rises is calcitonin. This peptide hormone functions to lower blood calcium levels by promoting the deposition of calcium into the bones. It achieves this by inhibiting osteoclast activity, which are the cells responsible for bone resorption, and stimulating osteoblasts, the cells that form new bone tissue.Calcitonin operates in conjunction with parathyroid hormone (PTH), which has the opposite effect by raising blood calcium levels when they fall too low. PTH enhances the reabsorption of calcium by the kidneys, stimulates osteoclast activity, and increases intestinal absorption of calcium through the effects of calcitriol. Together, calcitonin and PTH play crucial roles in maintaining calcium homeostasis in the body.