Circular muscular layer of stomach

The circular muscular layer of stomach is the middle layer of the muscularis externa of the stomach, lying between the outer longitudinal and inner oblique muscle layers. It is composed of circularly arranged smooth muscle fibres that encircle the stomach wall and work along with the longitudinal and oblique muscle fibres to help in mixing, churning, and propulsion of gastric contents.

The circular muscle layer is present throughout the stomach but becomes markedly thickened in the distal pyloric region, where it forms the pyloric sphincter. This sphincter surrounds the pyloric canal and regulates the passage of chyme from the stomach into the duodenum while preventing duodeno-gastric reflux.

Clinical correlate

Hypertrophic pyloric stenosis results from hypertrophy of this circular muscle, causing gastric outlet obstruction in infants.

Innervation

• Controlled by the enteric nervous system, particularly the myenteric (Auerbach's) plexus, which lies between the circular and longitudinal muscle layers.

• It's activity is modulated by autonomic nerves, wherein the parasympathetic innervation (via vagus) stimulating motility, while sympathetic innervation (via sympathetic trunk and coeliac plexus) inhibiting motility.