As a rule, researchers pay less attention to the features of the large intestine than to the small intestine. The purpose of the study was to determine the features of the microscopic structure of the rectum of ducks during the first year of the postnatal period of ontogenesis. For histological examinations, the material was selected from Ukrainian white-breasted ducks of 9 age groups: 1-, 3-, 7-, 14-, 21-day-old, 1-, 2-, 6-month-old and 1-year-old. Morphometric parameters of microstructures were set on cross sections of the midgut. The general change pattern in the morphometric parameters of the microstructures of the rectum of ducks was their increase, which was asynchronous and uneven. There was observed an active intestinal morphogenesis continued, as evidenced by the process of formation of villi and crypts in the group of 1-3-day-old ducks. The most intensive morphometric parameters of the rectum changed in the first month of the postnatal period of ontogenesis, during which – in the first week. In the first week, first and second month of life of ducks, the wall thickness of the rectum increased by 93.1, respectively; 199.5 and 20.4 %, the thickness of the mucous membrane – 81.0; 167.1 and 19.5 %, the thickness of the muscular membrane – by 126.1; 285.3 and 22.7 %, the height of the villi – by 113.2; 208.7 and 7.2 %, the width of the villi – by 84.7; 70.9 and 12.5 %, their surface area – by 293.8; 427.6 and 20.6 %, the depth of the crypt – by 85.1; 49.9 and 52.3 %, muscle plate thickness – by 254.0; 750.8 and 15.0 %. The most stable indicators of the rectum during the first year of the postnatal period of ontogenesis were the density of villi and crypts, the number of which after 7 days of age had no significant difference compared to that of a younger age. The indicates of adult birds morphometric parameters of the rectum of ducks corresponded at different ages: in 1-year-old – the thickness of the serous membrane and the density of villi; at 6 months – the diameter of the intestine, the surface area of the villi; at 2 months of age – the thickness of the wall and its mucous membrane, the width of the villi, the depth of the crypt; at 1 month – the thickness of the muscular membrane and plate, the height of the villi, the epithelium of the villi and crypt; at 3 days of age – the density of crypts; at 1 day of age – the width of the crypt.
The aim of the study was to determine the features of the topography and the number of the total population of endocrinocytes and enterochromaffin cells in the intestines of ducks during the first year of the postnatal period of ontogenesis. The experiments were performed on domestic ducks (Anas platyrhynchos domesticus) of black white-breasted breed (n = 5) 9 groups: 1-, 3-, 7-, 14-, 21-days-old, 1-, 2-, 6-month-old and 1-year-old. Determination of the total population of endocrine cells (argyrophilic) and enterochromaffin (argentaffin) was performed on histological specimens made from cross-sections of the middle section of the duodenum, jejunum, ileum, cecum and rectum, stained by Masson and Grimelius. The endocrine cells of 1- and 3-days-old ducks had a «superficial» location due to insufficient formation of crypts and villi. In older birds, in the duodenum, jejunum, and ileum, both argyrophilic and argentaffin APUD cells were localized mainly in crypts, and in the cecum and rectum, they were also in the epithelial layer of the villi. During the entire observation period, the highest content of both argyrophilic and argentaffin endocrinocytes in all intestines were found in 21-days-old ducks. Already at 3-days-old age, the total number of endocrine cells in various intestines corresponded to those of an adult bird. The highest number of argyrophilic and argentaffin endocrinocytes was found in the ileum and cecum, less in the rectum and jejunum, and the smallest number was in the duodenum. Enterochromaffin cells are the most common type of endocrinocytes in the ducks’ intestines, their relative content ranged from 40.1 to 97.5%. The highest relative content of argentaffin cells at 1-, 3- and 7-day-old was observed in the duodenum, at 14-day-old – in the duodenum and colon, at 21-day-old – in the rectum, at 1- and 2-month-old in jejunum, at the age of 6 month – in the duodenum, jejunum and caecum, and at the age of 1-year-old – in the ileum and cecum. In addition to argyrophilic endocrinocytes, which were located in the epithelium, other cells were found in the loose connective tissue of the villi base, the cytoplasm of which was also intensively impregnated with silver nitrate. Such cells were smaller and mostly oval in shape. Their cytoplasm was impregnated almost evenly around the nucleus and had no polarity in the location of the granules. Probably those were mast cells, which also contain bioamines, and, as well as enteroendocrinocytes, are found in the argyrophilic reaction.
According to the literature review, there have been paid less attention to the peculiarities of the large intestine of domestic birds than to the small intestine. The cecum is studied mainly in terms of their microbiome and assessment of the state of the immune system through the study of the structure and cell composition of lymphoid formations. Researchers note the role of the cecum in productivity, maintaining the health and well-being of animals. The aim of the paper was to study the features of the microscopic structure of the caecum of ducks in the first year of the postnatal ontogenesis period. Determination of morphometric parameters of microstructures was performed on histological specimens from a cross section of the middle caecum of ducks 1-, 3-, 7-, 14- and 21-days old, 1-, 2- and 6-month old and 1-year-old. Active morphogenesis of intestinal microstructures was observed in 1-3-day-old ducks, as evidenced by the process of villi and crypt formation. The older ducks, their main feature of the microscopic structure of the cecum anatomy was the increase with age of their morphometric parameters, which was uneven and asynchronous. However, the density of villi and crypts did not change with the age of the bird. The indexes of adult birds morphometric parameters of the ducks cecum corresponded at different ages: the diameter of the intestine, the thickness of the serous membrane, the density of villi, the depth of the crypt – In 1 year; villi width – In 6-month; the thickness of the intestinal wall, its mucous membrane, the density of villi, their surface area, the height of the epithelium of the crypt – In 1 month; the height of the villi and their epithelium, the thickness of the muscular membrane and muscle plate - in 21 days; width and density of crypts – at 3 days sold. The most intensive increase in morphometric parameters of the caecal microstructures occurred in the first month of the postnatal period of ontogenesis, during which they changed most rapidly in the first week.
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