The parathyroid glands, as the prefix "para" implies, lie at the side of the thyroid gland on the transverse or posterior side of the thyroid. They impart no effect on thyroid function but may be damaged by thyroid treatments because of their anatomic proximity.
Humans usually have four parathyroid glands that are responsible for regulating the calcium levels in circulation. If the thyroid gland needs to be surgically removed due to a cancerous growth or is treated with radiation, the parathyroid glands are occasionally damaged or even removed.
