The parathyroid glands is group of tiny glands that is located in the neck which controls the calcium levels of the body. This gland produces parathyroid hormone (PTH). This hormone raises the blood calcium level by breaking down the bone causing the release of calcium. It also increases the ability of the body to absorb calcium from the food that we eat and it increases the ability of the kidney to hold on to calcium that would be lost in the urine later on.
The regulation of calcium levels in the body is crucial for the heart, nervous system, kidneys and bones to function normally.
Therefore, the answer is parathyroid glands.