The Pyloric Sphincteric Cylinder in Health and Disease



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Chapter 5 (page 24)

The mucosal folds in the pyloric region can be demonstrated readily in the intact, living human stomach by radiographic techniques. Swallowing a few mouthfulls of a suitable barium sulphate suspension on the empty stomach, and applying graduated compression on the anterior abdominal wall, shows the folds to advantage (Chap. 13). By means of image intensification and TV monitoring the movements of the mucosal folds may be studied (Chap. 13).

The size of the folds is determined by the volume of the submucosa (Forssell l923, l934) and degree of distension of the lumen; increasing luminal distension causes progressive effacement of the folds. A similar but more pronounced effect is seen when contraction of the muscularis externa is abolished by the administration of anticholinergic substances, and simultaneous distension of the lumen obtained by means of air or gas insufflation. Under these circumstances macroscopic folds may disappear altogether. This principle is utilized in the upper gastrointestinal double contrast radiographic examination.

The position or direction of the mucosal folds during life depends mainly on the degree of contraction or relaxation of the muscularis externa. In his epic studies Forssell (l923, l934, l939) demonstrated "independent but co-ordinated" contractions of the muscularis externa and mucosa (brought about by contractions of the muscularis mucosae). One of the best examples of this phenomenon is seen during contraction of the pyloric sphincteric cylinder. Normally, when the cylinder is relaxed, its mucosal folds are circular; during contraction the folds change in direction, and with maximal contraction only longitudinal folds are seen in the fully contracted cylinder (Chap. 13).

When examining the surface of the gastric mucosa with a magnifying lens in the fresh specimen, it is seen to be divided into a multitude of small, slightly elevated polygonal areas by numerous linear depressions. These raised areas, which measure from 1.0 to 6.0 mm in diameter, are called the areae gastricae. On the surface of the areae gastricae numerous small tubular invaginations, the gastric pits or foveolae, are seen. It is into the bottom of these pits that the gastric glands open. Double contrast radiographic examination demonstrates the areae gastricae (Chap. 13). They are seldom visible endoscopically (Mcintosh and Kreel l977).

The mucous membrane of the first part of the duodenum, unlike that of the stomach, usually appears smooth, but on close inspection is seen to be thrown into rudimentary folds. Grossly visible crescentic mucosal folds (plicae circulares or valves of Kerckring) commence 2.5 to 5.0 cm distal to the pylorus, extending half to two-thirds of the way around the lumen.

Discussion

Two anatomico-functional divisions of the pyloric part of the stomach are clearly identifiable. The first, the muscular pyloric sphincteric cylinder, is a tube of thickened muscularis externa, approximately 3.0 to 5.0 cm in length when fully contracted (in adults). It is definable in morbid anatomical specimens, in which it is seen to end in an aboral thickening, the pyloric sphincteric ring (which forms the peripheral part of the pyloric ring) (Chap. 3, 11). The pyloric sphincteric cylinder is also clearly definable in radiographic motility studies during life (Chap. 13).

The second anatomico-functional entity in the distal stomach is the pyloric mucosal zone, containing mucus secreting and neuroendocrine cells. (Radiologically there are no differentiating features between the various mucosal zones). Unlike the cylinder, the mucosal zone may vary in extent in pathological conditions.

Anatomically the pyloric mucosal zone differs from the sphincteric cylinder in extent as well as in shape. In the normal stomach the mucosal zone is longer than the cylinder, especially on the lesser curvature. While the cylinder is roughly triangular in shape or fan-shaped, with the apex on the lesser and the base on the greater curvature (when contracted), the greatest length of the mucosal zone occurs on the lesser curvature (Fig. 5.1).

The entire sphincteric cylinder is lined by pyloric mucosa. Aborally both the mucosal zone and the cylinder end at the pyloric ring. At the oral end of the cylinder pyloric mucosa extends into the more proximal part of the stomach.

References

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