INTERIOR OF INTESTINE

The intestinal wall has four basic layers (from lumen outward):

1. Mucosa – absorption & secretion

   • Epithelium (simple columnar)
   • Lamina propria (connective tissue, vessels, lymphatics)
   • Muscularis mucosae

   Special features:

   • Villi (small intestine) → increase surface area
   • Microvilli → brush border
   • Intestinal glands (crypts of Lieberkühn)
2. Submucosa – support layer
   • Blood vessels, lymphatics
   • Meissner’s (submucosal) plexus
3. Muscularis externa – motility
   • Inner circular layer
   • Outer longitudinal layer
   • Auerbach’s (myenteric) plexus → peristalsis
4. Serosa / Adventitia – outer covering
   • Serosa (intraperitoneal parts)
   • Adventitia (retroperitoneal parts)

👉 Functionally important: Structure supports digestion, absorption, and peristalsis.