Understanding the Parathyroid Glands

The parathyroid glands are 4 pea-sized glands in the neck. They sit behind the thyroid gland. Their main job is to keep the blood calcium level in a healthy range. This helps muscles and nerves work correctly. It also keeps bones strong. When there is a problem with the parathyroid glands, the blood calcium level may get too high or too low. This has effects around the body.

Front view of neck showing voicebox (larynx), thyroid gland, parathyroid glands, windpipe (trachea), the laryngeal nerve, and the large blood vessels.

Back view of thyroid showing parathyroids.

How the parathyroid glands work

The parathyroid glands control the level of calcium and phosphorus in the blood by making parathyroid hormone (PTH). This is a chemical messenger that tells the body how to control calcium.

When blood calcium is low

When the blood calcium level is low, the glands make more PTH. This tells the body to increase the amount of calcium in the blood. To increase the blood calcium level, the body may absorb more calcium from food in the intestines. It may also take calcium from the bones and reabsorb more calcium from the urine.

When blood calcium is high

When the blood calcium level is high, the glands make less PTH. This tells the body to lower the amount of calcium in the blood. To lower the blood calcium level, less calcium is absorbed by the gut. Less calcium is taken from the bones. And more calcium is filtered out of the blood by the kidneys.