AMPHIBIAN PARATHYROIDS - MORPHOLOGICAL AND FUNCTIONAL-ASPECTS

Amphibians living partially or totally in a terrestrial environment ar e the first tetrapods to possess parathyroid glands. Purely aquatic am phibians and amphibian larvae lack these endocrine glands. The parathy roids develop at the time of metamorphosis. The parathyroid glands in caecilians consist of a single cell type, that of urodeles may be comp osed of basal (supporting) cells and suprabasal (chief) cells, and tha t of anurans of small and large chief cella Parathyroid glands of caec ilians and anurans lack connective tissue, blood vessels, and nerves. The parathyroid cells become activated in response to decreased blood calcium concentration and undergo changes indicating increased parathy roid hormone secretion. Increased blood calcium concentration suppress es secretory activity. Usually, parathyroidectomy elicits hypocalcemia in most amphibians. Such operations have no effect in lower urodeles. Parathyroid hormone administration provokes hypercalcemia in most amp hibians. The parathyroids of caecilians have not been studied in detai l. The urodeles and anurans exhibit seasonal changes in the parathyroi d glands. These changes may be initiated by environmental stimuli such as light, temperature, or alterations in blood calcium levels caused by natural hibernation. (C) 1995 Wiley-Liss, Inc.