Small

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 VilliBoth 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
• - enterocytes (with microvilli),
• - goblet cells,
• - paneth cells (SI only),
• - entero-endocrine cells,
• - M cells
• Lamina Propria
• - loose connective tissue
• - Peyers 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
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
• Peyers 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 Peyers 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

• Submucosa
• Connective Tissue
• Blood vessels
• Submucosal (Meissners) Plexus
• (Brunners glands in duodenum)
• Muscularis Externae
• 2 smooth muscle layers
• Inner - segementation
• Outer - peristalsis
• Myenteric (Auerbachs) Plexus b/t muscle layers

Submucosal Plexus
Myenteric Plexus
17
Layer 4 Adventitia/Serosa
Loose connective tissue