What is the primary action of calcitonin in the body?

The primary action of calcitonin is to inhibit the release of calcium from bones, which effectively lowers the levels of calcium in the blood. This hormone is produced by the parafollicular cells (C cells) of the thyroid gland in response to elevated blood calcium levels. By acting on osteoclasts, the cells responsible for bone resorption, calcitonin reduces their activity, leading to decreased calcium release from bones into the bloodstream.

Additionally, calcitonin also has effects on the kidneys, promoting a decrease in renal tubular reabsorption of calcium, thus promoting calcium excretion in the urine. However, its most significant role is to inhibit osteoclast activity, contributing to lower blood calcium levels.

The other options provided do not align with the primary function of calcitonin in the regulation of calcium homeostasis. For instance, stimulating calcium absorption or increasing osteoclast activity would result in higher calcium levels in the bloodstream, contrary to the action of calcitonin.