An Update on the Structure of the Parathyroid Gland

The parathyroid glands hold a special place in human anatomy, since they were the last major organ to be recognized by humans. The glands are recognized in all vertebrate animals higher than fish, and are derived from the pharyngeal pouches. The molecular signaling pathways that are involved in determining the differentiation of the glands are being elucidated. Studies in mice have demonstrated that the transcription factor encoded by Glial cells missing 2 (Gcm2) is a key regulator of parathyroid development. Recent studies indicate that the tetrapod parathyroid glands and the gills of fish are evolutionarily related structures, and that the parathyroid glands likely come into being as a result of the transformation of the gills during tetrapod evolution. The parathyroid chief cells play a central role in calcium homeostasis by sensing changes in extracellular calcium and releasing parathyroid hormone (PTH) to correct or maintain normal blood calcium levels. Chief cells undergo morphologic changes corresponding to different stages of the secretory cycle. Parathyroid oxyphil cells derived from chief cells as aging or some metabolic derangements, have the potential to produce PTH, PTH-related protein, and calcitriol. The existence of water-clear cells is confirmed in some kinds of animals, which may represent hyperfunction of the parathyroid gland. The presence of water-clear cell is associated with parathyroid hyperplasia or parathyroid adenoma. The molecular regulation of PTH synthesis and release indicates that parathyroid cells detect changes of the extracellular calcium levels by calcium-sensing receptor, which plays a central role in regulating PTH secretion.