PARATHYROID GLANDS

Slide # 196 - Four parathyroid glands are found on the posterior surface of the thyroid gland, 2 per lobe. These are small, bean-shaped epithelial organs, again derived from pharyngeal pouch endoderm.   Parathyroid glands are important in regulating serum calcium levels.   At low power, it is difficult to tell that the epithelial cells of the gland are arranged in cords.   At higher power, notice the clump-like arrangement of the secretory cells comprising the parathyroid.   They are of 2 types of cells: (1) The more numerous chief cells produce parathyroid hormone.   Chief cells are smaller and paler than the second cell type, oxyphil cells. (2) Less-frequently found are oxyphil cells, which are larger and more eosinophilic (because of lots of mitochondria).   Oxyphil cells tend to be present in groups or clumps.   Function is still unknown.