When blood calcium levels drop, glands embedded in the posterior thyroid secrete parathyroid hormone, which stimulates osteoclastic activity. It is made up of parathyroid glands that lie behind the thyroid glands. The reason why it is important because it controls calcium level in the blood and within the bones. It controlled by the low calcium levels in the blood it restorative parathyroid secretion whereas the high calcium levels in the blood stop the release of parathyroid hormone.