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HISTOLOGY OF THE GIT (cOnT….)
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GIT COMPOSITION
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The tubular part of the
GASTROINTESTINAL TRACT
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The tubular part of the digestive
• The tubular part of the digestive system consists of
esophagus, stomach, small intestine, and large intestine.
• The GIT has a common general plan of organization and
possesses four layers that are known as tunics.
– Tunica Mucosa (Lining epithelium, lamina
propria, muscularis mucosa)
– Tunica submucosa (In some part contains
submucosal glands)
– Tunica Muscularis (Muscularis externa)
– Tunica Adventitia/Serosa
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…tunica Mucosa
• Lining epithelium
– Varies from region to region
– Oesophagus & lower part of anal canal –
Stratified squamous non-keratinized
– Stomach – Simple columnar secretory in
function
– Small
intestine
–
Simple
columnar
absorptive, secretory, goblet cells present
– Large intestine – simple columnar, absorptive,
secretory, goblet cells present in large
numbers
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Oesophagus
• It is a tube about 25cm long extending
from the pharynx to the stomach.
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Oesophagus
• Tunica mucosa consists of the epithelium, underlying lamina
propria and muscularis mucosa. The lamina propria contains
lymphatic capillaries, blood capilaries, and loose connective
tissue. The muscularis mucosa is a thin, double layer of
smooth muscle, more substantial in the lower part of the
oesophagus
• Tunica submucosa is highly vascular, and contains loose
connective tissue. It contains oesophageal glands, that secrete
mucus to help ease the passage of swallowed food
• The muscularis externa layer in the top third of the
oesophagus contains skeletal muscle, in the middle, it is a
mixture of smooth and skeletal muscle, and in the bottom
third it is entirely smooth
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The stomach
Food starts to be digested and absorbed in the stomach,
although absorption is mostly limited to water, alcohol and
some drugs
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The stomach…
• The stomach is an expandable, muscular bag, and it
keeps swallowed food inside it by contracting the
muscular pyloric sphincter. Food can stay in the stomach
for 2 hours or more. Food is broken down chemically, by
gastric juice, and mechanically, by contraction of the
three layers of smooth muscle in the muscular externa
layer. The broken up food at the end of this process is
called chyme.
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Layers of the stomach
• This shows an image through the wall of the body of the
stomach at low power. You should be able to identify the
three major layers seen here - the mucosa, submucosa
and muscularis externa.
• The mucosa is full of gastric glands and pits, and there is
a prominent layer of smooth muscle - the muscularis
mucosa. The contraction of this muscle helps to expel the
contents of the gastric glands.
• The muscularis externa layer has three layers of muscle.
An innner oblique layer , a middle circular and an
external longitudinal layer. The contraction of these
muscle layers help to break up the food mechanically.
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• Gastric glands
Chief (zymogenic) cells.
–
Predominantly
located in the
body/base of the
gland. Secretes
pepsinogen.
•
Parietal (oxyntic)
cells
–
–
Larger than chief
cells. Concentrated
in the central half of
the gland.
Secretes
hydrochloric acid
and gastric
intrinsic factor
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…the stomach
(histological features)
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Small intestine
• It measures approximately 6.25m and it consists of
duodenum 0.25m, jejunum 2.4m, and ileum 3.6m
• Although these three parts have certain distinctive features,
the pattern of organization is the same and consists of the
same four coats as already described
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Duodenum
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Duodenum
• Between the intestinal villi there are the openings of simple
tubular glands, the crypts of Lieberkühn. One function of
the crypts of Lieberkühn is the secretion of "intestinal juice
Mucosa: It is lined with simple columnar epithelium
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Duodenum
• The principal cell types of epithelium of the small intestine
includes the Paneth cells, goblet cells, enterocytes, and
enteroendocrine cells
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…duodenum
• Lamina propria: It consists of loose connective tissue with
infiltrated lymphocytes in the form of solitary, nodules (unlike
Peyers patches of ileum); but in some places the lymphatic
nodules are aggregated. It also contains intestinal glands.
• Muscularis Mucosa: it consists of inner circular and outer
longitudinal layers of smooth muscles.
• Tunica submucosa:In the duodenum it contains branched
tubular glands known as Brunner’s glands which secrete
alkaline mucus that contains glycoproteins and
bicarbonate that help to neutralize the acids produced by
the stomach.
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Brunner’s Glands
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Jejunum
• Mucosa: It is lined with simple columnar epithelium
Unique features
– This is very similar to the duodenum except Brunner’s
glands are absent. Mucosa consists of simple columnar
epithelium with goblet
– Extensive villi are present as are the crypts of crypts of
Lieberkuhn.
– The pilcae cicularis are permanent folds in the intestinal
mucosa.
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Ileum
• Tunica mucosa: It is identified by the presence of the
lymphoid nodule known as payer’s patches in the lamina
propria of the mucosa.
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