Summary
The development of the endocrine and exocrine cells of Wistar rat pancreas was studied from day 16 through day 21 of gestation by ultrastructural observations. — A and B endocrine cells appeared immature on day 16 through day 18, being rich in free ribosomes and having relatively few and small secretory granules on day 16 and 17. These cells were dispersed among morphologically undifferenciated cells. On day 18, however, cells of this type were grouped into small islets. The maturation of the endocrine tissue starting on day 19 could be identified by the organization of the adult type of the islets (peripheral A cells) and by the development of the cellular ultrastructure, both being evident on day 20. In particular, the maturation of the B cells was indicated by the growing number of secretory granules, which were obviously more voluminous than in the earlier stages of development, and by the growth of the ergastoplasmic and Golgian structures. The maturation of the A cells was manifested by an increase in size and number of the secretory granules. —The morphologically differentiated exocrine cells were numerous on day 17. The zymogen granules were numerous from day 18 on. At the same time the size of the granules increased and the ergastoplasmic structures were clearly developed. Later, only minor ultrastructural modifications could be observed.
Résumé
L'observation ultrastructurale du pancréas des foetus de rats Wistar, âgés de 16, 17, 18, 19, 20 et 21 jours a permis d'étudier l'évolution du pancréas endocrine et exocrine au cours de la fin de la gestation. —Des cellules endocrines A et B présentant, par leur richesse en ribosomes libres, leurs granules sécrétoires relativement peu nombreux et de petite taille, un aspect peu mature sont à 16 et 17 jours dispersées parmi les cellules morphologiquement indifférenciées et à 18 jours groupées en petits îlots. La maturation du tissu endocrine amorcée à 19 jours se manifeste à 20 jours par l'organisation de type adulte des îlots (cellules A périphériques) et par l'évolution ultrastructurale des cellules. La maturation des cellules B se traduit par un enrichissement en granules sécrétoires, qui sont nettement plus volumineux qu'aux stades précédents, et un développement des structures ergastoplasmiques et golgiennes. Dans les cellules A la maturation se manifeste par une augmentation de la taille et du nombre des granules sécrétoires. — Les cellules exocrines morphologiquement différenciées deviennent nombreuses à 17 jours; mais ne sont riches en grains de zymogène qu'à partir de 18 jours. Cet enrichissement s'accompagne d'un accroissement de la taille des grains et d'un développement des structures ergastoplasmiques. Aux stades suivants l'évolution est discrète.
Zusammenfassung
Die Entwicklung der exokrinen und endokrinen Zellen des Pankreas von 16, 17, 18, 19, 20 und 21 Tage alten Föten wurde elektronenmikroskopisch untersucht. — Bis zum 18. Tag haben die endokrinen Zellen (A und B) noch ein unreifes Aussehen (verhältnismäßig wenig kleine Sekretionskörnchen und zahlreiche freie Ribosome). Am 16. und 17. Tag liegen sie spärlich zwischen morphologisch undifferenzierten Zellen, vom 18. Tage an bilden sie kleine Inseln. Das Reifen der endokrinen Zellen beginnt am 19. Tag und wird am 20. Tag mit dem Erreichen der beim Erwachsenen sichtbaren Insel-organisation, d.h. mit ihrer peripheren A Zellenlage besonders deutlich. Die Ultrastruktur der endokrinen Zellen verändert sich. Während die B Zellen eine Vermehrung der jetzt deutlich größeren Sekretionskörnchen und eine Ausdehnung des Ergastoplasmas und des Golgi Apparates vorweisen, zeigen die A Zellen eine Zunahme der Zahl und Größe der Sekretionskörnchen.— Die morphologisch vollentwickelten exokrinen Zellen werden am 17. Tag zahlreich. Am 18. Tag weisen sie eine Erhöhung der Zahl und Größe der Zymogenkörnchen auf und eine größere Ausdehnung des Ergastoplasmas. Nach dieser Zeit treten nur geringe strukturelle Veränderungen auf.
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Perrier, H. Evolution de l'ultrastructure du pancréas chez le foetus de rat. Diabetologia 6, 605–615 (1970). https://doi.org/10.1007/BF00418229
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DOI: https://doi.org/10.1007/BF00418229