The parathyroid glands are four pea-sized glands located onthe four corners of the thyroid gland. They secrete parathyroidhormone (PTH), which maintains calcium and phosphorushomeostasis. PTH regulates calcium such that when serumlevels of calcium fall too low, it increases the serum calciumlevel by stimulating more calcium release from the bones,increasing intestinal absorption of calcium and decreasingcalcium excretion into the urine. When the serum calciumnormalizes, the parathyroid gland shuts off the production ofPTH. An excess of PTH in the system throws off the calciumphosphorushomeostatic balance, resulting in various symptomsand clinical effects.