What is the primary action of calcitonin in the body?

Calcitonin is a hormone produced by the parafollicular cells (also known as C cells) of the thyroid gland, primarily involved in the regulation of calcium homeostasis in the body. Its primary action is to lower blood calcium levels by inhibiting osteoclast activity in the bones. Osteoclasts are the cells responsible for bone resorption, which is the process of breaking down bone tissue, leading to the release of calcium into the bloodstream. By inhibiting these cells, calcitonin effectively decreases the release of calcium from bones, thus reducing blood calcium levels.

Additionally, calcitonin also has an effect on the kidneys, where it can promote calcium excretion. However, the most significant action relevant to calcium regulation is its role in inhibiting osteoclast activity, which is why it is understood that it inhibits calcium absorption from the bones.

In the context of the other options, while some may suggest roles related to calcium absorption or retention, they do not accurately represent the primary function of calcitonin in the body’s calcium regulation system. Therefore, the underlying mechanism of calcitonin's action aligns with the role of inhibiting osteoclasts and, consequently, calcium resorption, leading to reduced blood calcium levels.