Intraluminal pressure studies in the stomach and duodenum showed an increase in pressure during peristaltic and segmental (phasic) contractions, with a simultaneous change in direction of the folds to longitudinal.
In vivo experimental studies showed that during luminal distension of the small bowel the folds were circular; appropriate electrical stimulation of the serosa caused contraction of the walls with stimultaneous change in direction of the folds to longitudinal.
Two anticholinergic substances (propantheline bromide and hyoscine-N-butylbromide) administered intramuscularly in therapeutic doses in normal, adult, informed volunteers caused the walls of the small bowel to relax (with consequent distension of the lumen), and a simultaneous change in direction of the folds to circular.
The oblique layer of the muscularis is clearly seen in the fundus and near the lesser curvature of the corpus, but the oblique fibers disappear distally (towards the antrum).
The outermost main layer is the serosa (Fig.
Nerve plexi provide the interface between the mucosa and the muscularis, as well as between the longitudinal and circular layers of the muscularis (9, 12).
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