Expansion
Inner oblique, middle circular and outer longitudinal
Expansion
From inside out:
- Inner oblique - unique to the stomach, incomplete, strongest near the cardia
- Middle circular - thickens at the pylorus to form the pyloric sphincter
- Outer longitudinal
Everywhere else in the gastrointestinal tract there are only two layers, inner circular and outer longitudinal. The additional oblique layer allows the stomach to churn as well as propel, mechanically breaking down food and mixing it with acid and pepsin.
Hypertrophy of the circular layer at the pylorus in infants produces infantile hypertrophic pyloric stenosis, with projectile non-bilious vomiting, a palpable olive and a hypochloraemic hypokalaemic metabolic alkalosis.