1. The Gastrointestinal System II: Small & Large Intestines
Histology SSN
March 7, 2005
Presented by:
Anne O’Donnell & Nadia Goodwin

2. 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

3. 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

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. 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
Myenteric (Auerbach’s) Plexus b/t muscle layers
Submucosal Plexus
Myenteric Plexus

6. Layer 4: Adventitia/Serosa
Loose connective tissue

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

8. Cells of 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

9. Cells of Mucosal Epithelium: Enterocytes
Terminal bar
Microvilli

10. Cells of Mucosal Epithelium: Enterocytes
Junctional complexes and terminal web
Terminal Bar

11. 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)

12. Cells of Mucosal Epithelium in SI: Paneth Cells
Located in Crypts of Lieberkuhn (bases of glands of SI b/t villi)
Secrete lysozymes
Basophilic base, eosinophilic granules at apex
Regulate bacterial flora of gut

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

14. 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

15. Lipid Absorption
Triglycerides and other lipids are packaged into droplets
Droplets are absorbed from lumen, then reach basolateral surface where they are released by excocytosis
Transported into lacteal

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

17. Duodenum
Characterized by submucosal Brunner’s Glands (protect duodenum by neutralizing stomach acid)

18. Duodenum vs Jejunum and Ileum
Submucosal Brunner’s Glands
No Brunner’s Glands

19. Large Intestine
Function: Reabsorbs water and electrolytes and eliminates undigested food and waste

20. Large vs Small Intestine
Similarities
Same Layers
Mucosa
Submucosa
Muscularis Externa
Adventitia/Serosa
Same Epithelial Cells
Enterocytes
Goblet cells
Enteroendocrine cells
M cells
BUT
Differences
Large Intestine has NO plicae circularis and NO villi
Large Intestine has MORE GOBLET cells
NO PANETH cells in LI

21. Large vs Small Intestine

22. Junction: Rectum and Anal Canal
simple columnar epithelium with goblet cells
glands
Recto-Anal Junction
-stratified columnar/ cuboidal epithelium
No glands

23. Recto-Anal Junction -stratified columnar/cuboidal epithelium - as move toward anus, more stratified squamous - at perineum, stratified squamous epithelia is keratinized

24. Stratified Columnar/Cuboidal
Stratified Squamous (non-keratinized)

25. Hemorrhagic Vessels
These vessels are in the submucosa of the anal canal. When dilated, they are internal hemorrhoids.
Hemorrhagic vessel

26. Internal Anal Sphincter
Inner circular layer of muscularis externa thickens to form internal anal sphincter

27. Question 1 The organ shown : Digests carbohydrates and proteins
Contains paneth cells
Reabsorbs water
Conjugates bile

28. Question 2
Villi are present in both images:
True
False

29. Question 3
Which sequence is the correct oral to anal order? B A D C