The Gastrointestinal System II:Small & Large Intestines
Histology SSN
March 7, 2005Presented by:
Anne O’Donnell & Nadia Goodwin
Small & Large Intestines
Small Intestine: principal site for digestion of food and absorption of the products of digestion
Large Intestine: reabsorption of water and elimination of undigested food and waste
4 Layers of Digestive SystemMucosa
- Epithelium
- Lamina Propria
- Muscularis Mucosae
Submucosa- Connective tissue, blood vessels,
submucosal plexus
Muscularis Externa- 2 muscle layers, myenteric plexus
Adventitia / Serosa- Loose connective tissue
Layer 1: Mucosal LayerEpithelium- 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
Layer 2: Submucosa & Layer 3: Muscularis Externae
Submucosa:
• 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
Myenteric Plexus Submucosal Plexus
Layer 4: Adventitia/Serosa
Loose connective tissue
Plicae Circularis vs VilliBoth 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
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
Cells of Mucosal Epithelium: Enterocytes
Terminal bar
Microvilli
Cells of Mucosal Epithelium: Enterocytes
• Junctional complexes and terminal web
Terminal Bar
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)
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
Cells of Mucosal Epithelium: Enteroendocrine Cells
• Secrete Hormones– GIP, CCK, Secretin
• Seen with silver stain• (Also in stomach)
Features of Mucosal Lamina Propria in SI
Lamina Propria: loose cellular connective tissue
Contains: 1. Peyer’s Patches: lymph
nodules and immune cells
2. Lacteals: endothelial-lined lymphatic channels w/in villi that uptake lipid droplets
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
Features of Muscularis Mucosae in SI
• Boundary b/t mucosa and submucosa
• Composed of two thin layers of smooth muscle
Duodenum
Characterized by submucosal Brunner’s Glands (protect duodenum by neutralizing stomach acid)
Duodenum vs Jejunum and Ileum
Submucosal Brunner’s Glands
No Brunner’s Glands
Large Intestine
• Function: Reabsorbs water and electrolytes and eliminates undigested food and waste
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
Large vs Small Intestine
Junction: Rectum and Anal Canal
Rectum -simple columnar epithelium with goblet cells-glands
-No glandsRecto-Anal Junction-stratified columnar/ cuboidal epithelium
Recto-Anal Junction-stratified columnar/cuboidal epithelium
- as move toward anus, more stratified squamous- at perineum, stratified squamous epithelia is keratinized
Stratified Columnar/Cuboidal
Stratified Squamous (non-keratinized)
Hemorrhagic Vessels
Hemorrhagic vessel
These vessels are in the submucosa of the anal canal. When dilated, they are internal hemorrhoids.
Internal Anal Sphincter
Inner circular layer of muscularis externa thickens to form internal anal sphincter
Question 1
The organ shown :a. Digests carbohydrates
and proteins
b. Contains paneth cells
c. Reabsorbs water
d. Conjugates bile
Question 2Villi are present in both images:
a. True
b. False
Question 3Which sequence is the
correct oral to anal order?
B
A
DC