chapter  1
42 Pages

Chemically-Induced Injury of the Parathyroid Gland: Pathophysiology and Mechanistic C onsiderations

ByCharles C. Capen

Parathyroid glands are composed of a single cell type concerned with the biosyn­ thesis of one hormone (Fig. 1). Chief cells have a normal secretory cycle, with the majority being in the inactive stage under steady-state conditions. In response to a low calcium ion signal, chief cells enter the active phase with syn­ thesis and packaging of a “batch” of hormone. After secretion of parathyroid hor­ mone (PTH), the chief cell involutes back to the resting (inactive) phase. In response to long-term stimulation, chief cells undergo a sequence of morphologic changes culminating in the formation of water-clear cells. Conversely, long-term suppression by elevated blood calcium ion results in parathyroids with predom­ inantly inactive and atrophic chief cells. Mitochondrion-rich oxyphil cells form in parathyroids of humans and certain animal species with advancing age. Syn­ thetic and secretory organelles are largely crowded out by the proliferation of mitochondria in the cytoplasm, suggesting that oxyphil cells are not actively involved in the biosynthesis of PTH.