Two pairs of small endocrine glands adjacent to the thyroid gland in the neck, which regulate calcium metabolism and maintain the normal excitability of the nervous system.The parathyroid glands secrete parathormone, which controls the body’s calcium-phosphorus balance. If the parathormone level is high, the calcium level is high and the phosphorus level low, and vice versa. This mechanism indirectly controls the amount of calcium deposited in bone as well as the functioning of the nervous system, since a low blood calcium level increases the irritability of nervous tissue. This means that if the gland does not produce enough hormone, the muscles begin to twitch and the reflexes are hypersensitive—and if the deficiency is severe the patient becomes afflicted with general tetany, muscle cramps, convulsions and emotional lability.