© 1967 by The Society for Integrative and Comparative Biology
Parathyroid Glands of Amphibians. I. Parathyroid Structure and Function in the Amphibian, with Emphasis on Regulation of Mineral Ions in Body Fluids
Department of Biological Sciences, De Paul University Chicago, Illinois 60614
Parathyroid glands of amphibians develop from the pharyngeal pouches and are located adjacent to the external jugular vein and hypoglossal nerve. They are composed of whorls of compact epithelial cells covered by a vascular capsule of connective tissue. Possibly two cell types are present: (a) peripheral clear cells, which are implicated in elaboration of hormone and contain secretory granules, and (b) dense reserve cells. During winter, the parathyroids undergo degeneration, characterized by morphological details which vary with the species; this is followed by regeneration in the spring. Parathyroidectomy may cause hyperexcitability, but rarely does tetanic death occur. Parathyroidectomized amphibians, like mammals, become hypocalcemic and hyperphosphatemic. In contrast to higher vertebrates, however, parathyroprivic anurans show an elevated urine phosphorus, which is presently interpreted as a reflection of the increased plasma load due to absence of a hormonally-induced, soft-tissue accumulation of phosphate. Further, parathyroidectomized frogs are hypercalciuric, possibly because of the lack of hormone-mediated mesonephric reabsorption. In both mammals and amphibians, treatment with exogenous parathormone induces hypercalcemia, hypercalciuria, and hypophosphatemia. The absence of change in the urine phosphorus content of hormone-treated frogs, associated with its decline in plasma, may be a consequence of metabolic variations based upon the heterothermic nature of the Amphibia.