Ken Richardson

The subject of this thesis is the structure and motility of the alimentary tract of the Tammar wallaby (Macropus eugenii). In the early part of the thesis the gross, topographical and microscopic anatomy of the alimentary tract, particularly as it relates to function, is described in some detail. Emphasis is placed on the structure of the ventricular groove, haustra and pylorus of the stomach. The remainder of the thesis reports on the investigation of movement and the related mixing and propulsion of digesta. Some observations of digesta movement were made using radiographic techniques which were then related to electrical events. Chronically implanted bipolar electrodes were used to record the extracellular electrical activity. A slow wave, with a frequency of 5.5 ± 0.1 cpm (mean ± s.e.m., between animals, n = 12), an amplitude of 120 ± 5.3 μV (mean ± s.e.m., n = 1000) and an aboral propagation of about 3 ± 0.07 mm per sec (mean ± s.e.m., between animals, n = 12) was recorded from all parts of the stomach. Action potentials were only recorded from the pylorus. Both slow waves and action potentials were recorded throughout the intestine. Two colonic slow wave frequencies were recorded. Possibly one was associated with antiperistaltic and the other with peristaltic activity. A pattern of myoelectrical activity, the migrating myoelectric complex was recorded moving from the duodenum to the ileum at about 90 minute intervals. The slow wave frequency of the duodenum was 26 ± 0.15 cpm (mean ± s e.m., between animals, n = 12) and on the ileum it was 25 ± 0.14 cpm (mean ± s.e.m , between animals, n = 12). The absence of a decrease in the frequency of the slow wave from the duodenum to the ileum is unique. Following transection and reanastomosis of the jejunum there was a marked drop in slow wave frequency below the surgical site. This suggests that the small intestine pacemaker may be at the duodenum