The parathyroid glands are several (usually four) tiny glands, located next to or behind the thyroid gland in the neck. They help control the amount of calcium in the blood. Normal calcium levels help maintain muscle control and the blood's ability to clot.
Enlarged parathyroid glands can cause excess levels of parathyroid hormone (hyperparathyroidism), which may lead to excess calcium in the blood. Surgery may be needed to treat this problem.
WebMD Medical Reference from Healthwise