What is the function of calcitonin in the body?

Calcitonin is a hormone produced by the parafollicular cells (C cells) of the thyroid gland, and its primary function is to decrease calcium levels in the blood. When calcium levels rise above normal, calcitonin is released into the bloodstream, where it acts to promote the uptake of calcium by bones and inhibit the activity of osteoclasts, the cells responsible for breaking down bone and releasing calcium into the bloodstream. This results in a net decrease in blood calcium levels.

Additionally, calcitonin may also reduce renal tubular reabsorption of calcium, leading to increased calcium excretion in the urine. The overall effect of calcitonin is to maintain calcium homeostasis in the body by lowering elevated calcium levels, thus providing a protective mechanism against hypercalcemia (high blood calcium levels).

In contrast, the other options refer to different physiological processes or hormones that are not related to the action of calcitonin. For instance, increasing blood calcium levels is primarily managed by parathyroid hormone (PTH) rather than calcitonin. Glucose uptake and protein synthesis are regulated by different hormones such as insulin and growth hormone, respectively, highlighting the distinct roles these substances play in metabolic processes.