Drawing of the Stomach ( Hypertrophic Pyloric Stenosis)

Drawing of a stomach and a part of the duodenum in gastric outlet stenosis. From left to right: First duodenal part, pylorus with long and narrow channel, and antrum which runs into the corpus of the stomach (M. Bettex). The hypertrophic muscle of the pylorus which increases mostly after birth and is demonstrated in the drawing as thickened ring muscle causes a gastric voiding disorder (= hypertrophic pyloric stenosis). The stomach tries to move the food and gastric content distally by vigorous peristaltic waves; nevertheless, the gastric content is moved backwards by a strong peristalsis (= retroperistalsis) and transported as a projectile forceful vomiting to the outside. Secondarily, the antral muscle thickens, followed by a dilatation of the stomach. The loss of fluid and electrolytes leads to exsiccosis, electrolyte and pH imbalance.