Muscular layer of stomach

The muscular layer of stomach (a.k.a. the muscularis externa) lies beneath the serosa and consists of three layers of smooth muscle fibres: an outer longitudinal, a middle circular, and an inner oblique layer. This three-layered arrangement is unique to the stomach and enables powerful mixing and propulsion of gastric contents.

• The longitudinal fibres form the outermost layer and are continuous with those of the oesophagus and duodenum. They are most prominent along the curvatures and function to shorten the stomach during peristalsis.

• The circular fibres form a complete middle layer around the stomach and become markedly thickened at the pylorus to form the pyloric sphincter, which regulates the passage of chyme into the duodenum.

• The oblique fibres, found mainly in the fundus and body near the cardiac region, constitute the innermost layer and provide an additional plane of contraction that enhances churning and mixing of food with gastric secretions.

Together, these muscle layers generate the peristaltic and mixing movements necessary for mechanical digestion and gastric emptying.