The Pyloric Sphincteric Cylinder in Health and Disease



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Chapter 2 (page 9)

mucosal folds within the distended region become circular (appearing transverse to the long axis of the bowel on the two-dimensional radiographic image) (Chap. 13). Whenever a peristaltic or segmental contraction occurs, all folds within the confines of the contraction change in direction to become longitudinal (Chap.13). This phenomenon was seen consistently in the distal stomach, duodenum, jejunum, ileum and with some modifications (due to its haustrations) also in the colon. 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. Injection of a cholinergic substance (neostigmine methylsulphate) in therapeutic doses caused an increase in the rate and intensity of peristaltic and segmental contractions in the small bowel; in all contracted regions the folds changed in direction to longitudinal.

Discussion

It appears that whenever a region of the gastrointestinal tract (e.g. the distal stomach or ileum) is distended, its mucosal folds are circular; when it contracts, the folds change in direction to become longitudinal, and in maximally contracted regions only longitudinal folds are seen. The phenomenon is seen both during peristaltic and "segmental" contractions.

It is concluded that peristaltic and segmental contractions are not limited to the external muscle layers of the wall; movements of the submucosal and mucosal layers, as expressed in characteristic and consistent movements of the mucosal folds, are an inherent component of these contractions. (A mucosal fold consists of a central core of submucosa with a layer of mucosa on both surfaces).

Seeing that a mucosal furrow exists between two adjacent mucosal folds, it is clear that longitudinal mucosal furrows are formed in this way, simultaneously with contraction of the outer muscular layers. It is surmised that the longitudinal intraluminal furrows or troughs will enhance flow of luminal contents, particularly when occurring simultaneously with contraction of the outer layers of the walls.

It is further surmised that the mucosal fold movements are brought about by actions of the muscularis mucosae. This presupposes an association between contractions of the muscularis externa and muscularis mucosae. As far as we are aware this has not been confirmed experimentally to date.

The mucosal fold movements mentioned above are probably one of the best examples of Forssell's (l923, l939) dictum that separate but co-ordinated movements of the muscularis externa and mucosa occur normally in the gastrointestinal tract (Chap 13).

Characteristic movements of the mucosal folds should be looked upon as an inherent component of peristalsis and segmental (or cylindrical) contractions, and should probably be included in their definitions. Even if this is endorsed, the definition of peristalsis will probably still be imperfect. For instance, little attention has been given to underlying myoelectric activity in the definition of peristalsis. The exact role of various regulatory peptides in peristalsis is awaiting further clarification.

The question also arises whether peristalsis should be differentiated from contractions which appear to be stationary but more segmental in nature, and which are associated with both propulsion and retropulsion of contents. In the present context cyclical contractions of the pyloric sphincteric cylinder are specifically referred to (Chap. 13). According to some authors these are of a "systolic" or "concentric" nature in man (Keet 1957) and in the "terminal antrum" of canines (Carlson et al. 1966). However, the elegant experimental investigations of Ehrlein (1980) and his associates (Pröve and Ehrlein l98l; Ehrlein and Akkermans l984) in canines and rabbits indicated that they might be due to extremely rapidly progressing, sequential contraction (i.e. peristaltic) waves.

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