The ultrastructural bases for coordination of intestinal motility
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The electrical control activity (slow waves) of dog small intestine is characterized by phase locking of potential changes in a frequency plateau in the upper intestine. In the distal intestine, phase locking does not occur, though frequencies of each segment are pulled up (increased) by adjacent, more proximal segments. This suggests poorer coupling in the distal compared to the proximal intestine. Electron microscopic studies of the intestine revealed no differences in appearance or number of nexuses (found only in circular muscle) or of intermediate contacts (found in both muscle layers) in duodenum and upper jejunum as compared with ileum. Thus, differences in cell to cell contacts could not explain poorer coupling in the ileum. No difference in innervation of these two regions was observed. However, evidence was obtained that circular muscle cells of the ileum, unlike those of the duodenum, are not oriented perpendicularly to the longitudinal muscle layer. This could provide a structural basis for poorer coupling and for the observed phase lag of potentials around the circumference of the ileum.
KeywordsElectron Microscopic Study Slow Wave Muscle Layer Cell Contact Longitudinal Muscle
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