PARATHYROID GLAND

PARATHYROID GLANDS

The four parathyroid glands (glandulae parathyroideae) are located in the capsule of a dorsal part of the thyroid gland. Each gland is encapsulated; tiny connective tissue septa divide the parenchyma of the gland into tiny lobules. The parenchyma itself consists of epithelial cells arranged in cords or groups. The predominant cells are referred to as chief (principal) cells. The chief cells measure approximately 8 μm, have a spherical nucleus and a light cytoplasm (containing glycogen). They produce parathormone, which they deliver from their secretory granules to adjacent fenestrated capillaries. Parathormone acts as a calcitonin antagonist, so that it raises blood calcium levels. The second population of epithelial cells are oxyphilic cells. As their name suggests, their characteristic feature is eosinophilia caused by the multiplication of mitochondria in the cytoplasm. Oxyphilic cells are larger than the chief cells. These cells do not appear until about 10 years of age. They have no secretory granules and therefore show no endocrine activity.

A more detailed description of the parathyroid glands is available in the e-course Endocrine System II .
The parathyroid glands are derived from the endoderm of the pharyngeal pouches. The lower pair, the glandulae parathyroideae inferiores, derive from the dorsal part of the 3rd pharyngeal endodermal pouches. The upper pair, superior parathyroid glands, is derived from the dorsal portions of the 4th pharyngeal endodermal pouches.