The Pyloric Sphincteric Cylinder in Health and Disease

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Chapter 11 (page 45)

Microscopic Anatomy

Illustrations of microscopic sections of the normal pyloric ring are occasionally encountered in published papers. In most instances the purpose is to illustrate some feature of the stomach in the vicinity of the pylorus and the ring is seen incidentally. On examining such illustrations the anatomical build of the ring may be studied.

Horton (l928) illustrated 3 normal stomachs sectioned 6 hours post-mortem. In all it is seen that the pyloric ring is not a structure consisting solely of muscular tissue. While its "base" is formed by muscularis externa, the top or inner part of the ring( i.e. the part surrounding the aperture) consists of a mucosal fold (made up of a core of submucosa with a layer of mucosa on each surface, as described in Chapter 5). In Horton's illustration of a 6 months old foetus the height of the outer muscular component of the pyloric ring is 14.0mm and the height of the inner mucosal fold, or mucosal component, also 14.0mm. In a 4 month old infant the muscular division of the ring measures 3.4cm in height and the mucosal division 2.0cm. In a one year old child the measurements are 3.5cm and 1.5cm respectively. It is clear in these subjects that the inner part of the pyloric ring consists of mucosal and submucosal, and not of muscular tissue.

Cole (l928) held that the abrupt interruption separating the lumen of the stomach from that of the duodenum (i.e. the pyloric ring) is a muco-membranous fold consisting solely of mucosa and submucosa with its acompanying muscularis mucosae. The circular fibres of the muscularis externa end at the base of the "pyloric fold", which should be looked upon as a valve and not as a sphincter, according to Cole (l928). Scott's (l946) observations led him to conclude that normally a thick mucosal fold caps the pyloric "sphincter" (from which it may be concluded that the ring consists of both the "sphincter" and an overlying mucosal fold).

In illustrations of Manning and Gunter (l950) the following measurements may be made: in a 66 year old subject the external muscular component of the ring is 3.0cm in height, and the inner mucosal/submucosal component 2.5 cm. In a 78 year old subject the figures are 2.5cm and 2.0cm respectively, and in a 58 year old subject 3.5cm and 2.0cm respectively. Williams (l962) illustrated two fresh, adult, partial gastrectomy specimens. In one the muscular component of the ring measures l8.0mm in height and the mucosal/submucosal component 9.0mm. In the other the figures are 21.0mm and 11.0mm respectively.

Present investigations

Although the nature and function of the pyloric ring is often debated, few deliberate attempts have been made to determine its microscopic anatomy. Consequently sections of the ring were done more than 6 hours post-mortem in 7 subjects varying in age from 9 months to 83 years, who had succumbed to non-gastrointestinal causes; a total of 20 sections were examined (Table 11.2). In all cases the pyloric ring is seen to consist of muscular and mucosal/submucosal components (Fig 11.3). For instance, in a 9 month old subject the muscular component is seen to be 2.0mm in height, and the overlying mucosal component 1.0mm. In a 5 year old subject the approximate figures are 5.5mm and 1.5mm respectively, and in a 44 year old subject 5.5mm and 1.5mm respectively.

Fig. 11.3. Microscopic section of normal pyloric ring. The muscular component measures 4.5 mm, the mucosal/submucosal component 1.5 mm in height

Table 11.2 Results of postmortem examination in seven subjects

SubjectAgeSexSpecimen numberTotal wall thickness (mm) Thickness of muscle layersThickness of mucosal/submucosal component


y = years
m = months


It is concluded that the pyloric ring consists of both muscular and mucosal/submucosal components. In anatomical specimens the muscular component accounts for approximately two-thirds of the total height of the ring, and the overlying mucosal/submucosal component for one-third. It is known that post-mortem autolysis of the mucosa sets in rapidly; Williams (l962) also pointed out that fixation diminishes the turgescence of the mucosal folds, contracts the stomach and reduces the submucosal space, so that sections after fixation are a poor representation of the living state. It may be concluded that the mucosal/submucosal component of the ring forms a more prominent part during life than would appear from microscopic sections.

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