The parathyroid glands are small glands, usually four in number, embedded within the back of the thyroid. These glands produce the hormone parathormone, which regulates the level of calcium and phosphorus in the blood and bones. Parathormone tends to increase the concentration of calcium in the blood by increasing bone breakdown.
This hormone has the opposite effect of calcitonin (thyrocalcitonin) which is secreted by the thyroid gland. Calcium plays an important role in many metabolic processes; too much calcium (hypercalcemia) or too little calcium (tetany) can disrupt the normal function of the muscles and nerves. Parathormone functions to help maintain homeostasis of blood calcium. The body’s cells are extremely sensitive to changing amounts of blood calcium.