Chapter 3 (page 12)

The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 3 (page 12)

Cunningham (l906) inferred that contraction of the circular fibres of the sphincteric ring would close the aperture. However, it was much more common to find the cylinder as a whole to be contracted. Under such circumstances the entire cylinder acted as a sphincter, closing the whole length of the pyloric canal against the entrance of material from the proximal stomach (Fig. 3.1A and B). This gave rise to the concept of a sphincteric cylinder.

Owing to the direction of their insertion into the sphincteric ring, it was thought that the longitudinal fibres acted as a dilator of the ring, i.e. of the pyloric aperture. In this sense the circular and longitudinal fibres seemed to be antagonistic.

Cunningham (1906) also inferred that the powerful musculature of the sphincteric cylinder had an important function, which was probably under control of a special innervation (Chap. 8). He noted that physiologists up to that time had not recognized the muscular sphincteric cylinder as a specialized region of the stomach.

In his classic anatomical studies, Forssell (l913) dealt almost exclusively with the human stomach, though some descriptions are found of the corresponding conditions in animals; the muscular structure of the stomach in relation to its forms of movement as seen during radiographic examinations, was studied extensively. Forssell (l913) found that the longitudinal (or vertical) part of the stomach consisted of two muscular regions, viz. the fornix and the corpus, and the transverse (or horizontal) part of two more, namely the sinus and canalis egestorius (Fig. 3.3). The muscular regions depended solely on the arrangement and thickness of the fibres of the various layers; the different regions were not separated from each other by sphincters or similar anatomical structures. (Comment: It is clear that Forssell's sinus and canalis egestorius correspond to Cunningham's vestibule and pyloric canal respectively).

Fig. 3.3. Muscular regions of stomach according to Forssell, F, fornix; C, corpus; S, sinus; C.E., canalis egestorius; M.A., membrana angularis; S.I., sulcus intermedius

On the duodenal side, however, a fibrous septum separated the circular muscle of the pylorus from the corresponding coat of the duodenum. Some of the pyloric longitudinal fibres were continuous with those of the duodenum. The longitudinal fibres on the lesser curvature, a short distance orally to the pyloric aperture, were weak or scanty, leading to an intermittent outpouching of the lumen called the membrana angularis (Fig 3.3).

Forssell (l913) looked upon the canalis egestorius as an anatomically preformed structure. On the greater curvature it extended from the sulcus intermedius to the pyloric aperture (Fig. 3.3). The sulcus intermedius, present in anatomical specimens, was due to tonic contraction at the entrance to the canalis, and not to an independent muscular structure. In anatomical specimens the distance from the sulcus intermedius to the pylorus was found to be 3.5 to 5.0 cm in non-contracted stomachs, and 3.0 to 4.5 cm in contracted ones. On the lesser curvature Forssell's canalis included part of the membrana angularis; he called the area between the latter and the pyloric aperture the "end piece".

The pyloric ring at the aboral end of the canalis was not a separate anatomical structure but formed part of the musculature of the canalis. However, Forssell stated that "this does not diminish, even in a small way, its anatomic or physiologic character as a sphincter" and that, on account of its anatomic structure, the pyloric ring could be looked upon as a proper sphincter, with both constrictor and dilator mechanisms.

During life the enire canalis contracted concentrically, an event which Forssell called the "annular wave". The contraction commenced more or less in the region of the sulcus intermedius, at a distance of 2.5 to 4.0 cm from the pylorus.

Horton (l928) studied the distribution and arrangement of the circular and longitudinal musculature in 90 normal, fresh post-mortem stomachs; this included the study of 5171 microscopic sections. An attempt was made to determine the percentage of circular and longitudinal fibres in the pyloric region which were continuous with the corresponding fibres of the duodenum. The circular musculature of the pyloric canal was found to be 4 to 5 times as thick as the longitudinal; it was broken up into incomplete bundles by connective tissue septa which entered the muscle from the submucosa and ran at right angles to the long axis of the lumen. The septa usually extended through the circular as far as the longitudinal layer; circular bundles formed in this way were not separate rings, but anastomosed freely with one another.

Of 84 specimens examined, 81 showed a complete break between the circular muscle of the pyloric region and that of the duodenum; this was confirmed in 97 percent of 1210 microscopic sections. The break between the two circular coats, caused by a septum of connective tissue and blood vessels, was up to 1.5mm wide, but as a rule somewhat narrower than this. A few minor variations were encountered; in 3 cases, for instance, a small quantity (less than 2 percent) of pyloric circular fibres were carried over into the duodenum for a short distance. The circular musculature of the duodenum, which was much thinner than that of the pylorus, began on the distal aspect of the connective tissue septum.