Amphibian parathyroids: morphological and functional aspects.
Microsc Res Tech
; 32(2): 79-90, 1995 Oct 01.
Article
em En
| MEDLINE
| ID: mdl-8580512
ABSTRACT
Amphibians living partially or totally in a terrestrial environment are the first tetrapods to possess parathyroid glands. Purely aquatic amphibians and amphibian larvae lack these endocrine glands. The parathyroids develop at the time of metamorphosis. The parathyroid glands in caecilians consist of a single cell type, that of urodeles may be composed of basal (supporting) cells and suprabasal (chief) cells, and that of anurans of small and large chief cells. Parathyroid glands of caecilians 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 parathyroid hormone secretion. Increased blood calcium concentration suppresses secretory activity. Usually, parathyroidectomy elicits hypocalcemia in most amphibians. Such operations have no effect in lower urodeles. Parathyroid hormone administration provokes hypercalcemia in most amphibians. The parathyroids of caecilians have not been studied in detail. The urodeles and anurans exhibit seasonal changes in the parathyroid glands. These changes may be initiated by environmental stimuli such as light, temperature, or alterations in blood calcium levels caused by natural hibernation.
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Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Anuros
/
Glândulas Paratireoides
/
Urodelos
Limite:
Animals
Idioma:
En
Ano de publicação:
1995
Tipo de documento:
Article