Parathyroid hormone
The parathyroid glands, of which there are 4–6, are found on the back of the thyroid glands, and secrete parathyroid hormone, This causes an increase in blood calcium levels by targeting bone, the intestine, and the kidneys. The parathyroid hormone is the antagonist of calcitonin. Parathyroid hormone release is triggered by falling blood calcium levels and is inhibited by rising blood calcium levels.