Answer: Calcitonin
Explanation:
When calcium levels in the blood is low, Parathyroid hormone is released to increase it. On the other hand, when calcium levels are high and need to be decreased, Calcitonin is secreted.
Calcitonin acts in opposition to PTH by inhibiting osteoclasts (a cell from which bone develops), stimulating osteoblasts, and increasing the excretion of calcium into the urine by the kidneys. [lumencandela]
