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The development degree of mammals at birth is markedly variable especially between placental and non-placental species. In marsupial mammals the organogenesis is completed during a period called external gestation, when the young animal remains at the maternal pouch being breastfed for, on average 90 days. This study reported the relevant morphological features found in the pancreas of the Brazilian opossum Didelphis aurita, a marsupial mammal, during its intramarsupial development. Newborns and young opossums removed from the pouch were divided into groups according to their average body length. The animals with few hours of intramarsupial life had visibly immature pancreas, due to the presence of early arrangement of endocrine and exocrine components. There was an only very large pancreatic duct, and blood vessels full of nucleated erythrocytes. In the individuals who were in the second third of intramarsupial development, the exocrine components were arranged in developing acini and endocrine cells were found arranged in early islets. The presence of connective tissue and the division of the organ into lobes became more evident at this stage. In the last third of the external gestation, we found better structured acini with relatively small lumens. The islets were well-organized, and the presence of connective tissue around them was the most evident. Morphometric analyses showed considerable variations in the proportion of pancreatic structural components between the stages of intramarsupial development, indicating that marsupial pancreas undergoes morphological modifications and grows during the period of external gestation.
The development degree of mammals at birth is markedly variable especially between placental and non-placental species. In marsupial mammals the organogenesis is completed during a period called external gestation, when the young animal remains at the maternal pouch being breastfed for, on average 90 days. This study reported the relevant morphological features found in the pancreas of the Brazilian opossum Didelphis aurita, a marsupial mammal, during its intramarsupial development. Newborns and young opossums removed from the pouch were divided into groups according to their average body length. The animals with few hours of intramarsupial life had visibly immature pancreas, due to the presence of early arrangement of endocrine and exocrine components. There was an only very large pancreatic duct, and blood vessels full of nucleated erythrocytes. In the individuals who were in the second third of intramarsupial development, the exocrine components were arranged in developing acini and endocrine cells were found arranged in early islets. The presence of connective tissue and the division of the organ into lobes became more evident at this stage. In the last third of the external gestation, we found better structured acini with relatively small lumens. The islets were well-organized, and the presence of connective tissue around them was the most evident. Morphometric analyses showed considerable variations in the proportion of pancreatic structural components between the stages of intramarsupial development, indicating that marsupial pancreas undergoes morphological modifications and grows during the period of external gestation.
A complex network of nerve fibers of the enteric nervous system and enteroendocrine cells is known to regulate the gastrointestinal tract. The distribution and frequency of the argyrophil, argentaffin and serotonin immunoreactive endocrine cells and of the submucosal and myenteric nervous ganglia were studied in the small intestine of the capybara Hydrochoerus hydrochaeris, aiming to verify the existence of possible numerical correlations between endocrine cells and nervous ganglia. Fragments of the duodenum, jejunum and ileum of adult animals were collected and processed according to routine histological techniques. To study the nervous ganglia, hematoxylin and eosin staining was used, while specific staining techniques were used to study the argyrophil, argentaffin and serotonin immunoreactive endocrine cells: Grimelius, modified Masson-Fontana and peroxidase anti-peroxidase, respectively. Endocrine cells were more abundant in the area of the crypts and, in relation to their morphology, ‘open type’ endocrine cells prevailed. The population of argyrophil cells was larger than that of argentaffin cells, and these cells were larger than serotonin immunoreactive cells. The frequency of endocrine cells was apparently greater in the duodenum, indicating the importance of this intestinal segment in digestive and absorptive functions. Prominent nervous ganglia were observed in the submucosal and myenteric plexi, and were larger and more frequent in the myenteric plexus. A numerical correlation was found among the endocrine cells (argentaffin and serotonin immunoreactive cells) and the myenteric nervous ganglia, suggesting the presence of physiological interactions among the endocrine and nervous systems for the control of intestinal activities. The findings in this study contribute to the understanding of the digestive processes of this species, which may also help in its conservation and future survival.
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