Closure of the Pylorus

Abstract

1. The anatomical arrangements of the submucosal layer at the pylorus have been examined and the attachment of mucosa to muscle at the pylorus has been emphasised. 2. It is argued that because of this attachment, contracttion of the muscularis mucosae will pull up mucous membrane into the pyloric ring to form a plug which occludes the lumen. This plug can be seen in a proportion of gastrectomy specimens, where it forms a watertight seal. Movements of the mucosa without affecting the muscularis propria can be shown to “open” and “close” the pylorus. 3. A hypothesis of closure of the pylorus by this plug is advanced, and reasons given that although it is a low-pressure closure, it is sufficient to obstruct the low pressure emptying of the stomach and hence explain some radio-logical observations. 4. Closure of the whole pyloric canal by the fan-shaped muscle is described and this produces high intra-luminal pressure with an action like a mechanical press, squirting fluid forwards and backwards out of the canal. 5. It is believed that the pylorus also closes at high pressure during duodenal cap contraction as a barrier to reflux into the stomach.