1. Small & Large Intestines
Large Intestine: reabsorption of water and elimination of undigested food and waste
Small Intestine: principal site for digestion of food and absorption of the products of digestion

2. 4 Layers of Digestive System
Mucosa
- Epithelium
- Lamina Propria
- Muscularis Mucosae
Submucosa
- Connective tissue, blood vessels, submucosal plexus
Muscularis Externa
- 2 muscle layers, myenteric plexus
Adventitia / Serosa
- Loose connective tissue

3. Plicae Circularis vs Villi Both are present in the small intestine as specializations to maximize absorptive surface area
Plicae Circularis: circular folds w/in a core of submucosa. Contains many villi.
Villus: finger-like mucosal projections w/in a core of lamina propria

4. Layer 1: Mucosal Layer Epithelium Lamina Propria Muscularis Mucosae
- enterocytes (with microvilli),
- goblet cells,
- paneth cells (SI only),
- entero-endocrine cells,
- M cells
Lamina Propria
- loose connective tissue
- Peyer’s Patches
- lacteals
Muscularis Mucosae
- Boundary b/t mucosa and submucosa
- 2 layers of smooth muscle

5. Mucosal Epithelium: Enterocytes
Absorptive Cells
Columnar cells with basal nuclei
Microvilli on apical surface
Digestive enzymes in microvilli glycocalyx (breakdown sugars & proteins)
Junctional complexes and terminal web

6. If stain with PAS, will see the
Glycocalyx
Macrophages
Mast cells

7. Mucosal Epithelium: Enterocytes
Terminal bar
Microvilli
The terminal web contains actin filaments in a dense network of spectrin molecules overlying a layer of intermediate filaments. Cell organelles are excluded from this terminal web and in this perparation is it relatively unstained.
Terminal web

8. Cells of Mucosal Epithelium: Enterocytes
Terminal Bar

9. Cells of Mucosal Epithelium: Goblet Cells
Produce mucus
Interspersed among enterocytes
Appear empty because mucus is washed out in slide preparation
(more goblet cells in colon than SI)

10. Cells of Mucosal Epithelium in SI: Paneth Cells
Located in Crypts of Lieberkuhn (bases of glands of SI b/t villi)
Antibiotic: Secrete lysozymes
Regulate bacterial flora of gut

11. Cells of Mucosal Epithelium in SI: Paneth Cells
Located in Crypts of Lieberkuhn (base of glands of SI b/t villi)
Basophilic base (cytoplasm), eosinophilic granules at apex

12. Cells of Mucosal Epithelium: Enteroendocrine Cells
Secrete Hormones
GIP, CCK, Secretin
Seen with silver stain
(Also in stomach)

13. Features of Mucosal Lamina Propria in SI
Lamina Propria: loose cellular connective tissue
Contains:
Peyer’s Patches: lymph nodules and immune cells
Lacteals: endothelial-lined lymphatic channels w/in villi that uptake lipid droplets
M Cells: more squamous epithelial cell (overlies the Peyer’s Patch). No microvilli.

14. Features of Mucosal Muscularis Mucosae in SI
Boundary b/t mucosa and submucosa
Composed of two thin layers of smooth muscle

15. 4 Layers of Digestive System
Mucosa
- Epithelium
- Lamina Propria
- Muscularis Mucosae
Submucosa
- Connective tissue, blood vessels, submucosal plexus
Muscularis Externa
- 2 muscle layers, myenteric plexus
Adventitia / Serosa
- Loose connective tissue

16. Layer 2: Submucosa & Layer 3: Muscularis Externae
Connective Tissue
Blood vessels
Submucosal (Meissner’s) Plexus
(Brunner’s glands in duodenum)
Muscularis Externae:
2 smooth muscle layers
Inner - segementation
Outer - peristalsis
Myenteric (Auerbach’s) Plexus b/t muscle layers
Submucosal Plexus
Myenteric Plexus

17. Layer 4: Adventitia/Serosa
Loose connective tissue