Final answer:
Calcitonin decreases the reabsorption of calcium in the kidneys, leading to increased calcium excretion in urine and a decrease in blood calcium levels.
Step-by-step explanation:
When calcitonin is produced in response to high levels of calcium in the blood, its effect on calcium homeostasis involves several actions. One of the key effects is on the kidney. Calcitonin decreases the reabsorption of calcium in the kidneys, leading to an increase in the excretion of calcium in the urine. Consequently, this action contributes to lowering the levels of calcium in the bloodstream, returning it towards normal levels. Calcitonin also suppresses the activity of osteoclasts (bone-resorbing cells) and, in contrast to parathyroid hormone (PTH), works to decrease the release of calcium from bones.