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    Biomimetic gastric tract simulator : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Engineering at Massey University, Manawatu, New Zealand
    (Massey University, 2023) Olson, Gerald
    Mimicry of the biomechanical functioning of the human gastric tract can play a significant role in study of the behaviour of foods and food structures as they are broken down and digested in the human body. The gastric tract wall produces peristaltic waves and other deformation patterns providing movement, accommodation, mixing and evacuation of foods in the stomach and connected gastric tract organs. This thesis presents an advanced biomimetic dynamic in vitro model of the human gastric tract that simulates anatomic geometry and demonstrates the mixing and movement of gastric tract contents. Materials, methods, and techniques suitable for mimicking the gastric tract wall were investigated and artificial membrane layers, artificial muscles, muscle activation and control mechanisms, and feedback sensors were developed and integrated into a dynamic physical model of the gastric tract. A composite material of silicone rubber reinforced with a nylon elastic fabric provides a thin, watertight, and highly elastic artificial membrane that forms the shell of the tract. Artificial muscles made from loops of coiled nylon monofilament line, attached to the artificial membrane, are contracted, and expanded through the pulling and releasing of flexible tendons or cables. Contraction and expansion of the artificial muscles is carried out using winding mechanisms and motors, while feedback and control systems track and maintain the desired mechanical activity of the tract. Mimicry of the muscle and membrane layers of the gastric tract wall is a novel approach to simulating gastric tract biomechanics, resulting in a soft, highly flexible, and dynamic physical in vitro modelling of the geometrical, anatomic, and biomechanical functioning of the human gastric tract.
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    A radiological study of the patterns of contraction and digesta movement in the alimentary tract of the sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Veterinary Science at Massey University
    (Massey University, 1981) Wyburn, Robert Sharp
    A radiological study of the motility of the stomach and small intestine and the movement of their contents was undertaken to define, in detail, the forms of contractions and their effect on digesta. A variety of radiographic techniques were employed depending on the information sought. For continuous observation over extended time periods fluoroscopy was used which combined image intensification with a closed circuit television chain and video-tape recorder. For detailed analysis of contractions or movements radiographic cine-film, serial spot-films or plain radiographs were used. The radiographic contrast of digesta was enhanced by the addition of barium sulphate which was either administered orally or introduced to a particular site through a fistula or cannula. Stainless steel wire loops sutured into particular structures formed radio-opaque markers of sites of specific interest. In the study of the small intestine the electrical activity of the intestinal wall was recorded in conjunction with the radiographic techniques. The sequential contractions of the compartments, folds and pillars of the reticulo-rumen that comprise A and B sequences were found to be the result of waves of contraction migrating across reticulo-rumen caudally from the reticulum and cranially from the caudal ventral blind sac. The different character of A and B sequences in the fasted and replete animal reflected waves of contraction that migrated at different speeds over varying distances. The pattern of digesta flow within the reticulo-rumen followed a consistant pattern suggesting that the selection of digesta for onward passage to the omasum was by flotation. The pattern of gas movement suggested that the displacement of gas from the dorsal rumen into the caudal ventral blind sac initiated B sequences of contraction. No movement of the omasum was observed radiographically other than that imposed by contiguous structures, especially the reticulum. The most prominent feature of abomasal motility was peristaltic contractions moving towards the pylorus at a frequency which remained constant irrespective of the degree of abomasal distension. Abomasal distension was found to inhibit A sequences in the reticulo-rumen and to alter the pattern of digesta movement in the small intestine. The presence of peristaltic contractions on the abomasum was related to activity in the duodenum and orad jejunum. The movement of digesta in the small intestine was of two basic forms; patterns of movement that were characteristic for a particular region and migrating patterns of movement. These patterns were associated with the electrical activity recorded from the intestinal wall. Alterations to the flow of digesta through the small intestine caused by increased flow through the pylorus, additions or subtractions through T cannulae or the insertion of re-entrant cannulae at certain sites caused marked changes in the patterns of digesta movement. It was concluded that the basic motility pattern in both the stomach and the small intestine is migrating waves of contraction. The pattern in which these waves occur results from interactions between (a) the flow of digesta, (b) the degree of distension either local or in adjacent regions and (c) the pace-setter - imposed via the vagus, on the reticulo-rumen and by the slow wave frequency on the abomasum and small intestine.
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    Endocrine cells in the gastrointestinal tract of sheep : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Histology at Massey University
    (Massey University, 1985) Gurnsey, Michael Peter
    Previous investigations have shown that the digestive activities of the mammalian GI tract are controlled, in part at least, by biologically active compounds released from endocrine cells in the mucosa of the GI tract itself. Despite this, comparatively few studies have been made of the endocrine cells in the GI tract of sheep. There is also a paucity of information about the suitability and reliability of histochemical and immunohistochemical methods for the identification of GI endocrine cells in sheep. The aims of this study were to: (a) establish reliable techniques for identifying endocrine cells in the GI tract of sheep, (b) use these techniques to investigate the effects of age on the distribution and densities of various GI endocrine cells, and (c) investigate possible changes in endocrine cell densities due to infection with the helminth parasite Trichostrongylus colubriformis. Initially, various histochemical and immunohistochemical staining techniques were investigated for their suitability for identifying endocrine cells in mucosal samples from reticulum, rumen, body and antral regions of the abomasum, three duodenal sites, ileum, colon and caecum, as well as the pancreas, of adult animals. As a result, the De Grandi technique was selected to estimate argyrophilic cell densities, EC cells were identified by the fast garnet technique, and ECL cells by their silver staining and morphological characteristics. The PAP immunohistochemical technique was used to identify G, S, and A cells, using antisera to gastrin, secretin, and pancreatic glucagon, respectively. No endocrine cells of any type were found in the reticulum or rumen. Argyrophilic cell densities were greatest in the abomasal body and proximal duodenum, then decreased distally. EC cell densities were highest in the duodenum, although, like argyrophilic cells, they were found throughout the abomasum and intestines. In contrast, ECL cells were confined to the abomasal body. Greatest densities of G cells occurred in the abomasal antrum and proximal duodenum; they were absent from the abomasal body, ileum and large intestine. S cells were confined in their distribution to the small intestine. Pancreatic islets of Langerhans contained A cells, as well as cells with slight argyrophilia; the identity of the latter cells was not determined. A cells were also found in exocrine acini, but these were the only cells in the exocrine portion of the pancreas that were stained by any of the histochemical or immunohistochemical techniques used. No A cells were identified in the mucosa of the GI tract. These studies also clearly established that ovine G cells are not argyrophilic. This finding is in contrast to those reported for most mammalian species with a simpler form of stomach. The effects of age on endocrine cell densities were studied using the tissues from 100 - 110 day old foetuses, 2 week and 24 week old lambs, and adult sheep. All endocrine cell types identified in adult sheep were also present at the other ages. However, in the foetuses, endocrine cell densities were lower than in other age groups. The most notable age-related trend was that antral G cell densities increased with increasing age. In contrast, from 2 weeks of age, there was a decrease in intestinal G cell densities with increasing age. It was also clear that D cell densities were much higher in 2 week old lambs than for any other age group. Possible explanations for these age-related changes in endocrine cell densities are discussed. D (somatostatin containing) cells were located throughout the abomasum and intestines of all nonadult animals and in pancreatic islets of 2 and 24 week old lambs. The effects on endocrine cell densities of an experimental infection with 40,000 T. colubriformis larvae was investigated in 40 week old lambs. Although the resultant infestation was mild, there was a significant (P<0.001) increase in argyrophilic cell densities in the proximal small intestine. Specific identification of the argyrophilic cell type(s) which had increased was not possible, however, the most likely candidates were D1, X and K cells. It was concluded from these studies that endocrine cells, similar in morphology and staining characteristics to those of other mammalian species, occur within the mucosa of the abomasum, small and large intestine of sheep. Greatest densities of endocrine cells occur in the abomasum and proximal duodenum. Cell types identified in the GI tract included EC, ECL, G, S and D cells, while D and A cells were identified in pancreatic islets. It was demonstrated that endocrine cell densities change with age and that significant changes in cell densities can occur in mild trichostrongylosis.