11. Esophagus and Stomach.pdf

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Naveen Sooknanan McGill Fall 2011
1
Esophagus and Stomach:
Before we discuss the Esophagus in particular, it would be useful to make a general plan of the
digestive tract starting with the esophagus and ending in the large intestines
The mucosa is made of three layers:
o The epithelium, the cell make-up changes depending on the structure
o The lamina propria is made of loose irreg. CT
o The muscularis mucosae is made of 2 layers of
SMCs
The inner layer is circumferential and
the outer layer runs in parallel with the
organ
Cutting a cross section of the
organ, the inner layer will be in
long. section and the outer layer
in cross section
This layer can vary in thickness
The submucosa is either loose or dense irreg. CT which can vary in thickness depending
on the organ
The muscularis (not muscularis mucosa) is another layer contains 2 sublayers of SMCs
o There is an inner circular and outer longitudinal layer, just like the MM
(muscularis mucosae)
o The stomach also contains a 3rd layer, which is oblique
The last layer is the serosa, or the adventitia, which is dense irreg. CT (aw always)
Note that just like in any other system we studied, these components are not present
everywhere
The esophagus is the first component of the digestive
tract we will look at after the oral cavity (we won’t
discuss the pharynx)
Mucosa:
o The epithelium is a nonkeratinized
squamous stratified epithelium
This allows for the esophagus to
be wet, allowing food to slide
down easily
o The lamina propria is loose CT
o The muscularis mucosa is only ONE layer of
longitudinal SMCs
This layer varies in thickness
depending on how far down you go
The muscularis is the most dense in
the esophagus in comparison to the
entire digestive tract
Submucosa:
o Dense irreg. CT
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Naveen Sooknanan McGill Fall 2011
2
o Contains esophegeal glands, which are exocrine mucous secreting glands (i.e.
secrete into lumen)
The ducts of these glands can be seen in the lumen
Their secretions help make the epithelial lining slippery to help food slide
down
Muscularis:
o Contains 2 layers of SMCs, an inner circular and an outer longitudinal layer
These layers can be distinctly
seen by taking a cross section of
the esophagus
Adventitia:
o Dense irreg. CT
o Surrounds the adventitia and continues
all the way to the skin
Remember, we said most
adventitias are continuous with
one another
The stomach is a segment of the digestive system which looks more like a bag than a tube. The
main function of the stomach is to add an acidic fluid (pH of
2.0) into food, turning it into a viscous mass called chyme
The acidic nature helps activate certain enzymes which
are only active in acid. These enzyme help break down
food into chyme
The stomach also secretes an intrinsic factor which is
crucial to the absorbance of the vitamin B12
The stomach also produces hormones such as gastrin
o This is the only one we need to remember,
although the stomach secretes around 12
hormones
The layers of the stomach are as follows:
Mucosa:
o The epithelium is a simple columnar
epithelium with secretory mucous cells
This epithelium infolds to form
gastric glands with two
regions: the pit and the gland
These folding allow to
increase the surface
area of the stomach,
helping digestion of
food occur faster
The pit is composed of surface
mucous cells
The gland section can be divided into the neck and the base
SS = stratifies squamous (epithelium)
D = duct of esophegeal gland
GL = secretory portion of the esophegeal gland
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