Muscular layer of small intestine

The muscular layer of small intestine (a.k.a. muscularis externa) is composed of two layers of smooth muscle fibres:

• An inner circular layer

• An outer longitudinal layer

Between these two layers lies the myenteric (Auerbach's) plexus, which contains autonomic nerve fibres and ganglion cells that regulate intestinal motility.

The coordinated contraction of the circular and longitudinal muscle layers produces segmentation movements, which mix intestinal contents with digestive secretions, and peristaltic movements, which propel chyme distally along the gastrointestinal tract.

Histological Arrangement (Lumen → Exterior)

• Mucosa

• Submucosa

• Muscularis externa (muscular layer of small intestine)

  • Inner circular smooth muscle

  • Myenteric (Auerbach's) plexus

  • Outer longitudinal smooth muscle

• Serosa (or adventitia in retroperitoneal parts of the duodenum)

Clinical correlate

Damage to the myenteric plexus can impair intestinal motility, leading to disorders such as intestinal pseudo-obstruction and contributing to conditions like Hirschsprung's disease (aganglionosis of the enteric nervous system).