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
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
Layer 1: Mucosal Layer
Epithelium
- 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 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
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 in SI:
Paneth Cells
• Located in Crypts of
Lieberkuhn (base of
glands of SI b/t villi)
• Basophilic base,
eosinophilic granules at
apex
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.
2.
Peyer’s Patches: lymph
nodules and immune cells
Lacteals: endotheliallined lymphatic channels
w/in villi that uptake lipid
droplets
Features of Mucosal 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
Recto-Anal Junction
-stratified columnar/
cuboidal epithelium
-No glands
Recto-Anal Junction
-stratified columnar/cuboidal epithelium
- as move toward anus, more stratified squamous
- at perineum, stratified squamous epithelia is keratinized
Anal Transition Zone
Stratified
Columnar/Cuboidal
Anal Stratified Squamous Epithelium
Hemorrhagic Vessels
These vessels
are in the
submucosa of
the anal canal.
When dilated,
they are
internal
hemorrhoids.
Hemorrhagic
vessel
Question 1
The organ shown :
a. Digests carbohydrates
and proteins
b. Contains paneth cells
c. Reabsorbs water
d. Conjugates bile
Question 2
Villi are present in both
images:
True or False
Question 3
Which sequence is in the
correct oral to
rectum/anal order?
B
A
D
C