The parathyroid glands are divided into four structures located behind the thyroid glands. They are responsible for secreting parathyroid hormone (PTH), which serves to increase blood calcium levels. The main sources of calcium are bone demineralization and intestinal absorption. Hypersecretion of PTH may result in bone loss and renal stones. Osteoporosis which is more commonly found in post-menopausal women has been linked to estrogen and its effects on PTH.