BIOL 2420 Lecture Notes - Lecture 4: Muscularis Mucosae, Muscular Layer, Intestinal Epithelium
26 Apr 2018
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Unit 9 – Lecture 4
The GI Tract Wall Has Four Layers
- structure of GI wall is similar in stomach and intestines
o variations exist from one section of the GI tract to another
- gut wall is crumpled into folds to increase surface area
o rugae – the name of the folds in the stomach
o plicae – the name of the folds in the small intestine
o villi – small fingerlike extensions of intestinal mucosa that project into the lumen
- additional surface area is added by tubular invaginations of the surface that extend down into the
supporting connective tissue
o gastric glands – the name of the invaginations in the stomach
o crypts – the name of the invaginations in the intestine
o deepest invaginations form secretory submucosal glands that open into the lumen through
ducts
- four layers of the gut wall
1. inner mucosa – facing the lumen
2. submucosa
3. muscularis externa – layers of smooth muscle
4. serosa – covering of connective tissue
Mucosa
- the inner lining of the GI tract
- has 3 layers
o single layer of mucosal epithelium facing the lumen
o lamina propria – sub epithelial connective tissue that holds epithelium in place
o muscularis mucosae – thin layer of smooth muscle
- structural modifications increase the amount of mucosal surface area to enhance absorption
1. the mucosal epithelium
o most variable feature of the GI tract
o changes from section to section
o cells of the mucosa include:
▪ transporting epithelial cells – enterocytes in the small intestine
▪ endocrine and exocrine secretory cells
▪ stem cells
o at the apical surface of the epithelium cells secrete:
▪ ions
▪ enzymes
▪ mucus
▪ paracrine molecules into the lumen
o on basolateral surface of the epithelium
▪ substances absorbed from the lumen and molecules secreted by epithelial cells
enter the ECF
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