Parathyroid disorders are conditions that affect the functioning of the parathyroid glands. These glands are part of the endocrine system, which regulates various body functions by producing and releasing hormones. Generally, four pea-sized parathyroid glands are found on the back of the butterfly-shaped thyroid gland, which is in the neck slightly below the Adam’s apple. Occasionally parathyroids are found within the thyroid gland, in the thymus (an immune system gland in the chest), or other places in the upper chest and neck. Sometimes people have more or fewer than four parathyroids.

The parathyroids regulate the amount of calcium in the bloodstream. When the calcium levels drop, the glands are stimulated to create parathyroid hormone (PTH). This hormone triggers bones to release calcium into the blood and increases the amount of calcium that is absorbed by the kidneys, thus reducing the amount lost in urine. PTH also triggers the kidneys to produce calcitriol, a form of vitamin D that allows the intestines to absorb more calcium.

Calcium is vital to many bodily functions, including the development and maintenance of bones and teeth. Calcium is also involved in the transmission of nerve signals and contraction of muscle fibers. Too much calcium (hypercalcemia) or too little calcium (hypocalcemia) can cause complications in the kidneys, bones and nervous system.

PTH is also involved in regulating levels of phosphorus in the body. As with calcium, phosphorus levels are adjusted depending on how much of the mineral is in the body. For example, if there is too much phosphorous, PTH limits absorption of phosphorus by the kidneys, which reduces the amount of phosphorus in the blood. Phosphorus is present in every cell in the body, and a surplus or deficiency can affect many of the body’s systems.

Although the parathyroid glands are involved in regulating both calcium and phosphorus, complications caused by parathyroid disorders are usually associated only with increases or decreases in calcium.