There are four parathyroid glands located behind the thyroid gland in your neck. These glands secrete parathyroid hormone which helps regulate the calcium level in your body. Calcium is an essential mineral that functions to maintain your bone strength, healthy teeth, muscle function, nerve function, normal clotting of the blood, and the regulation of hormones and enzymes. One or more of your parathyroid glands can become hyperactive and release an excess amount of parathyroid hormone into your bloodstream. The resulting abnormally high calcium level in your blood may cause low bone mineral density (called osteopenia or osteoporosis), bone fractures, kidney stones, abdominal pain, constipation, and mood changes such as depression. If you suffer from hyperactive parathyroid glands, known as hyperparathyroidism, your physician will refer you to a surgeon for removal of one or more of your parathyroid glands. After your surgery, your calcium levels will return to normal, and your symptoms will resolve.