The parathyroid glands are different than the thyroid gland, even though the names are similar. The four parathyroid glands are usually on the back of the thyroid gland, but they can be located around the jaw or neck.
Parathyroid glands secrete a hormone called PHT. The PHT regulates the exchange of calcium between the blood and the bones. When the parathyroid gland is over active, too much calcium is pulled out of the bones. This is called hyperparathyroidism or parathyroid disease.
Bones need calcium for strength. The brain needs calcium to think and muscles need calcium to contract. Too little calcium in the bones will cause a serious condition called osteoporosis (brittle bone disease). Too much calcium in the blood increases the risk of having a stroke and can make people feel sick.