The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 3 (page 11)

According to Cunningham (l906) the demarcation of the cardiac and pyloric portions of the stomach is indicated on the lesser curvature by a notch or elbow-like band, the incisura angularis. The position of the incisura is not constant and is influenced by the degree of filling of the stomach; at some stages it may disappear altogether. The pyloric portion is subdivided into two parts, viz. the pyloric vestibule (the oral division) and the pyloric canal (the aboral division) (Fig. 3.1A). The vestibule and canal meet at the sulcus intermedius, a faint but very constant furrow on the exterior of the greater curvature, 2.5 to 3.0 cm proximal to the pyloric aperture. In other words, the pyloric canal extends from the sulcus intermedius to the pyloric aperture, while the vestibule is located on the oral side of the sulcus. On the exterior of the lesser curvature no demarcation between the canal and vestibule is evident in adults, but the subdivision is clear in the interior of the stomach.

No part of the stomach is more definite or more distinct than the pyloric canal, according to Cunningham (l906). It consists of a tubular or cylindrical thickening of the muscularis externa, approximately 3.0 cm in length; it is also called the pyloric cylinder. When the cylinder is contracted, it forms the pyloric canal (Fig. 3.1B), which is best demonstrated in the foetus or the child, and in adult specimens hardened in formalin. The canal is usually contracted along its whole length; when contracted, the lumen is obliterated by closely packed longitudinal mucosal folds.

Fig. 3.1. A. Divisions of pyloric region according to Cunningham. P.S.C., pyloric sphincteric cylinder; P.V., pyloric vestibule; P.A., pyloric aperture; S.I., sulcus intermedius. B Contracted pyloric sphincteric cylinder according to Cunningham. P.C., pyloric canal; P.V., pyloric vestibule; P.A., pyloric aperture; S.I., sulcus intermedius

At the pyloro-duodenal junction the aboral margin of the muscular cylinder is increased in thickness, thereby forming the massive muscular ring which encircles the pyloric aperture. Cunningham (l906) called this ring the pyloric sphincteric ring (Fig. 3.2). The ring protrudes into the commencement of the duodenum; when viewed from the duodenal side, it presents as a smooth, rounded knob with a small puckered opening, the pyloric aperture, in its centre.

The pyloric sphincteric ring is not a separate anatomical structure, but constitutes a localized thickening of the cylinder, according to Cunningham (1906). On the gastric or oral side, the circular fibres of the ring merge imperceptibly into those of the cylinder, without any demonstrable anatomical boundary between the ring and cylinder. On the aboral or duodenal side conditions are completely different. Here the circular fibres of the ring are sharply demarcated from those of the duodenum by a fibrous septum; this ensures a complete break between the circular musculature of the pylorus and that of the duodenum (Fig. 3.2).

Fig. 3.2. Diagram of pyloric musculature according to Cunningham. P.S.C., pyloric sphincteric cylinder; P.S.R., pyloric sphincteric ring; F.S., fibrous septum; C.D.M., circular duodenal musculature; L.M., longitudinal musculature; C.M., circular gastric musculature; S.I., sulcus intermedius

Not only the circular, but also the longitudinal fibres are present in greater mass in the cylinder than in any other part of the stomach. In contrast to the circular fibres, a certain percentage of gastric longitudinal fibres is continuous with those of the duodenum. The more superficial fibres of the gastric longitudinal coat extend across the pyloro-duodenal junction to merge with those of the duodenum. The deeper longitudinal fibres, as they approach the pyloric aperture, dip into the sphincteric ring; some of these become interwoven with the circular fibres of the ring, while others extend through the circular coat to reach the submucosa.

On the oral side of the cylinder both its circular and longitudinal fibres merge imperceptibly into those of the remainder of the gastric wall. Except for the palpable thickening of the cylinder, and the shallow sulcus intermedius, no anatomical division can be demonstrated on the oral side of the cylinder between its musculature and that of the vestibule.

Cunningham (1906) called the muscular cylinder the pyloric sphincteric cylinder. The aboral thickening, but integral part of the cylinder, was the pyloric sphincteric ring (Fig. 3.2). Contraction of the cylinder caused formation of the pyloric canal, which had to be distinguished from the pyloric aperture.

He found minor variations in the arrangement of both circular and longitudinal muscle fibres in different specimens. In one specimen for instance, all the longitudinal fibres dipped into the sphincteric ring, while some superficial circular fibres of the ring were carried on to the duodenum for a short distance. Sometimes the deeper longitudinal fibres interlaced with the superficial circular fibres of the ring, forming a feltwork of mixed fibres which was carried on to the duodenum. These variations soon gave way to the proper coats of the duodenum, and in most specimens the arrangement was as indicated above.

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