The parathyroid glands are small, pea-sized glands located behind the thyroid gland in the neck. Typically, there are four parathyroid glands, and their primary function is to regulate the body's calcium levels. They produce a hormone called parathyroid hormone (PTH), which helps control calcium and phosphate balance in the blood and bones. When calcium levels in the blood drop, the parathyroid glands release PTH, which stimulates the release of calcium from bones, increases calcium absorption in the intestines, and reduces calcium loss in urine. This regulation is crucial for maintaining healthy bones and proper functioning of the nervous and muscular systems.