The human species has four parathyroid glands, which adhere to the back of the thyroid.
Parathyroids produce the parathyroid hormone, responsible for increasing the level of calcium in the blood.
Parathyroid hormone deficiency
Parathyroid hormone deficiency causes a decrease in the amount of calcium in the blood, which causes skeletal muscle cells to contract convulsively.
If the person affected by this deficiency is not treated with administration of parathyroid hormone or calcium, muscle tetany and death may occur.