Parathyroid glands are small oval-shaped endocrine glands, measuring 5 mm and weighing 130 mg. Mammals possess 2 pairs, located on the posterior surface of the thyroid gland. They regulate one of the most important elements in the human body, calcium.
Calcium is critical for the conduction of electricity through our nervous system, muscle contraction and the strength of our bones. In order to regulate the blood levels of calcium the parathyroid glands secrete parathyroid hormone (PTH). A low level of calcium in the bloodstream triggers the release of PTH which in turn causes the calcium stored in bones to get released into the bloodstream as well as an increase in uptake from the food we eat. When in abundance the excess calcium gets stored in our bones. Calcium is the only mineral with its entirely own regulatory system and it is kept at a very specific range at all times.