GLOSSARY

The intestinal wall is a four-layered structure that, like the rest of the gut, consists from inside to outside of the mucosa, submucosa, muscularis, and serosa, and is responsible for digestion, absorption, motility, and immune defence.

Layers

• Mucosa: columnar epithelium, lamina propria, and muscularis mucosae; the site of absorption and secretion.
• Submucosa: connective tissue with vessels, lymphatics, and the Meissner’s (submucosal) plexus.
• Muscularis externa: an inner circular and outer longitudinal layer with the Auerbach’s (myenteric) plexus between them.
• Serosa: the visceral peritoneum; in retroperitoneal parts it is replaced by adventitia.

The Enteric Nervous System

About 400–600 million neurons in the Meissner’s and Auerbach’s plexuses control motility and secretion even without the brain; it is sometimes called the “second brain”.

The Intestinal Barrier