Download Digestive System: Esophagus, Stomach, Small and Large Intestines

Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
Digestive System: Esophagus, Stomach, Small and Large Intestines
General Plan of the Digestive System
• Hollow tube extending from oral cavity to rectum
• Wall exhibits basic organization of the entire tube
1- Mucosa: Composition
• Covering epithelium
• Loose connective tissue called lamina propria
• Smooth muscle layer muscularis mucosae, with inner circular and outer longitudinal
layers
2- Submucosa
• Dense irregular connective tissue layer with blood vessels, nerves, and lymphatic vessels
• Contains submucosal nerve plexus that controls muscularis mucosae
3- Muscularis Externa
• Thick, smooth muscle layer inferior to submucosa
• Normally contains an inner circular and an outer longitudinal smooth muscle layers
• Myenteric nerve plexus located between inner and outer muscle layers
• Myenteric nerve plexus controls motility of smooth muscles in muscularis externa
4- Serosa or adventitia
SEROSA
ADVENTITIA
Thin layer of connective tissue, mesothelium, Thick layer of connective tissue, doesn’t
that covers the visceral organs
have mesothelium layer
Covers abdominal esophagus, stomach, small Covers thoracic part of esophagus and
intestine, and anterior wall of colon
posterior wall of ascending and
descending colon
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Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
i.
Esophagus
• Soft tube that extends from pharynx to stomach,
posterior to the trachea
• Penetrates diaphragm and enters stomach
• Lumen lined by nonkeratinized stratified squamous
epithelium
• In the upper third, muscularis externa contains skeletal
muscle
• In the middle, both smooth and skeletal muscle found in
muscularis externa
• In lower third,muscularis externa contains smooth
muscle
• Mucous esophageal glands are present in both the
lamina propria and submucosa for lubrication
• Adventitia surrounds the esophagus in the thoracic
cavity
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Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
• Muscularis mucosae and submucosa from esophagus
continue with those of stomach layers
ii.
Stomach
• Transition from esophagus to stomach is abrupt and
from stratified squamous to simple columnar (lined by
mucus-secreting simple columnar epithelium for
protection
• Receives, stores, mixes, and digests (converts)
ingested food (bolus) products to form semiliquid
chyme
• Consists of cardia, fundus, body, and pyloric regions
• Surface pitted by gastric pits, which are connected to
gastric glands in the lamina propria (In pylorus, gastric
pits are deeper than in fundus or body)
• Gastric glands produce gastric juices rich in
hydrochloric acid and protein-digesting enzymes
• Muscularis externa shows internal oblique, middle
circular, and outer longitudinal muscle layers
• Fundus and body form the major regions, and are
histologically identical
• Submucosal and myenteric nerve plexuses regulate
peristaltic Activity
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Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
• Rugae are formed during contraction of muscularis mucosae, as the stomach fills, the
rugae disappear and form a smooth mucosa, When stomach contract or empty, rugae seen
in the wall
Gastric Glands and Cells
1- Mucous Neck Cells
•
secrete an alkaline mucus to protect the stomach
lining from acidic gastric juice
2- Chief Cells
•
secrete the inactive enzyme called pepsinogen;
pepsinogen is activated to pepsin by:
3- Parietal Cells
•
secrete hydrochloric acid (HCl) which helps
convert pepsinogen into pepsin and kills
microbes in food
•
secretes intrinsic factor which helps with
absorption of vitamin B12
4- G Cells (Enteroendocrine Cells)
secrete several hormones and substances like
gastrin, histamine, somatostatin, endorphins
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Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
iii.
Small Intestine
• Long, convoluted tube divided into duodenum,
jejunum, and ileum
• Duodenum is the shortest segment with broad,
tall, and numerous villi
• Digests gastric contents and absorbs nutrients into
blood capillaries and lymphatic lacteals
→ Amino acids, water, ions, glucose and other
substances are absorbed and transported in
blood capillaries
→ Long-chain fatty acids and monoglycerides are
transported by lymphatic lacteals
• Contains numerous permanent surface modifications that
increase cellular contact for absorption
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Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
Structural modifications of the small intestine wall increase surface area
1- Plicae circulares are spiral folds with submucosa core that
extend into intestinal lumen
2-
Villi: are fingerlike projections of lamina propria that
extend into the intestinal lumen, which contain a core of
connective tissue with capillaries, lacteal, and smooth
muscle strands (smooth muscle contribute in vilus
movement by contraction)
3-
Microvilli: are cytoplasmic extensions of absorptive cells
that extend into intestinal lumen, which are coated with
brush border enzymes that digest food products before
absorption
Q/ Compare between villi and microvilli?
microvilli
villi
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Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
Cells of Small Intestine
1- Absorptive cells with microvilli in intestinal epithelium.
2- Goblet cells, interspersed between absorptive cells.
3- Enteroendocrine cells are scattered throughout the epithelium and intestinal glands
4- Paneth cells with pink eosinophilic granules in cytoplasm are located in the intestinal
glands, these cells produce lysozyme to control microbial flora in intestine
5- Microfold cells are specialized cells that cover the lymphatic Peyer’s patches
Glands of Small Intestine
1- Intestinal glands located between villi throughout the small intestine, which open into the
intestinal lumen at the base of the villi
2- Duodenal glands in the submucosa of duodenum are characteristic of this region, Duodenal
glands penetrate muscularis mucosae to discharge mucus and bicarbonate secretions,
Bicarbonate secretions enter base of intestinal glands and protect duodenum from acidic
chime
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Assistant lecturer: Ali Maki Hamed
Dijla University College
Histology lect5 2nd grade
Faculty of Dentistry
Lymphatic accumulations in Small Intestine
Peyer’s patches are numerous aggregations of permanent lymphatic nodules, which found
primarily in the lamina propria and submucosa of terminal part of intestine (ileum), Overlying
Peyer’s patches are specialized M cells, which are not anywhere else in the intestine, M cells
show deep invaginations that contain macrophages and lymphocytes, M cells sample intestinal
antigens and present them to underlying lymphocytes for response
iv.
Large Intestine (Colon)
The large intestine is situated between the anus and the terminal end of the ileum. It is
shorter and less convoluted than the small intestine. It consists of an initial segment
called the cecum, and the ascending, transverse, descending, and sigmoid colon, as well
as the rectum and anus.
Chyme enters the large intestine from the ileum through the ileocecal valve.
Unabsorbed and undigested food residues from the small intestine are forced into the
large intestine by strong peristaltic actions of smooth muscles in the muscularis
externa. The residues that enter the large intestine are in a semifluid state; however, by
the time they reach the terminal portion of the large intestine, these residues become
semisolid feces.
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