The correct option is C.
The parathyroid hormone and calcitonin hormone are the ones responsible for regulating the level of calcium in the blood. Â Calcitonin which is secreted by the thyroid gland inhibits osteoclasts and stimulates osteoblasts thus decreasing blood calcium level.
The parathyroid hormone which is secreted by parathyroid glands inhibits osteoblasts and stimulates osteoclasts. It also reduces the output of calcium by the kidney and promotes the absorption of calcium at the small intestines, thus increasing the blood calcium level.
