Download 212-Digestive System..

DIGESTIVE SYSTEM

3 major components:
1. Oral cavity.
2. Alimentary canal.
3. Associated Glands:
• Salivary glands.
• Liver.
• Pancreas.
Wall of the Alimentary Canal
Four concentric layers:
1. Mucosa:
– Epithelial Lining:
• Simple columnar
epithelium (in stomach &
intestine).
– Lamina propria:
• Connective tissue.
• It contains mucosal glands.
– Muscularis mucosae:
• 2 layers of smooth muscle
cells.
Serosa
Wall of the Alimentary Canal
2. Submucosa:
Connective tissue containing
blood vessels & nerves. May
contain glands (as in
duodenum).
3. Muscularis Externa:
2 smooth muscle layers:
• Inner circular layer.
• Outer longitudinal layer.
4. Serosa:
Connective tissue covered by
mesothelium (simple squamous
epithelium).
Serosa
STOMACH

It has 4 regions:
cardia, fundus, body
and pylorus.
fundus
cardia
body
pylorus
Fundus of Stomach

Mucosa:
Shows gastric pits in which
open the fundic glands.
– Epithelial lining: simple
columnar epithelium
(mucus-secreting).
NO goblet cells.
– Lamina propria: Connective
tissue containing numerous
fundic glands.
– Muscularis mucosae: 2
layers of smooth muscle.
Fundus of Stomach

Submucosa:
– Connective tissue containing
blood vessels & nerves.
– NO glands.

Muscularis Externa:
– 3 smooth muscle layers:
• Inner oblique.
• Middle circular.
• Outer longitudinal.

Serosa:
– Connective tissue covered by
mesothelium.
Fundic Glands
Simple branched
tubular glands.
 Have short narrow
ducts (pits).
 Numerous;
occupying most of
the lamina propria.
 Perpendicular to
the surface.

Fundic Glands
Composed of 5 cell types:
1. Parietal cells: secrete HCl and
gastric intrinsic factor that
helps absorption of vitamin B12.
2. Peptic (chief) cells:
secrete pepsin.
3. Mucous neck cells:
secrete mucus.
4. Enteroendocrine cells:
secrete hormones.
5. Stem cells: regenerative cells.
SMALL INTESTINE


It has 3 regions:
duodenum, jejunum and
ileum.
To increase surface area
the mucosa has:
– Villi.
– Crypts (intestinal glands).
Duodenum
1. Mucosa:
Shows villi and crypts.
– Epithelium: simple
columnar epithelium
with goblet cells.
– Lamina propria:
Connective tissue
containing intestinal
glands (crypts).
– Muscularis mucosae:
2 layers of smooth
muscle cells.
Duodenum
2. Submucosa:
– Connective tissue
containing blood vessels
and nerves.
– Contains Brunner’s
glands (secrete mucus).
3. Muscularis Externa:
– 2 smooth muscle layers:
• Inner circular layer.
• Outer longitudinal layer.
4. Serosa:
– Connective tissue
covered by mesothelium.
Intestinal Glands (Crypts)


Simple tubular glands
that open between villi.
Composed of 5 cell types:
1. Columnar cells:
absorptive.
2. Goblet cells: secrete
mucus.
3. Paneth cells: secrete
lysozyme (antibacterial).
4. Enteroendocrine cells:
secrete hormones.
5. Stem cells: regenerative
cells.
LARGE INTESTINE

It is composed of:
– Appendix,
– Cecum,
– Colon (ascending, transverse,
descending & sigmoid),
– Rectum, and
– Anal canal.
Colon
1. Mucosa:
Shows only crypts (NO villi)
– Epithelium: simple columnar
epithelium with numerous
goblet cells.
– Lamina propria: Connective
tissue containing numerous
crypts. Cells of the crypts are
the same as in small intestine
but NO Paneth cells.
Lymphatic nodules: frequent.
– Muscularis mucosae:
2 layers of smooth muscle.
Colon
2. Submucosa:
– NO glands.
3. Muscularis Externa:
– Inner circular & outer
longitudinal smooth muscle
layers.
– The longitudinal layer is not
continuous but in the form of 3
ribbons (teniae coli).
4. Serosa:
– C.T. covered by mesothelium.
– Has fat-filled pouches called
appendices epiploicae.
PRACTICAL SLIDES
Fundus of Stomach
Duodenum
Colon
Fundus
of Stomach
Duodenum
Colon