GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 1 of 8
Histology: Esophagus & Stomach
I.
Introduction
A.
The digestive system consists of 6 components: the oral cavity, mouth,
esophagus, small intestines, rectum, and anus
B.
Additional components of the digestive system include the salivary glands,
liver and pancreas
C.
The primary function of the digestive system is to obtain the molecules
required from ingested food for maintenance, growth and energy needs of
the body
D.
Thus, food particles are broken down to their individual units (e.g. amino
acids), these molecules are absorbed and moved to the blood system where
they are transported to the various organs and tissues within the body.
II.
General Plan of the Intestinal Wall
A.
The gastrointestinal tract (all 6 components) is a hollow tube surrounded
by 4 principal layers: (from innermost to outermost)
1.
mucosa/mucous membrane
2.
submucosa
3.
muscularis externa
4.
serosa or adventitia
B.
The mucosa consists of 3 regions which include the epithelium, lamina
propria, and muscularis mucosa
1. Epithelial lining
a.
stratified squamous or columnar
b.
may be protective, absorptive or secretory.
c.
functions as a selectively permeable barrier between the
contents of the lumen and the tissues of the body
i.
facilitates transport and digestion of food
ii. promotes the absorption of the products of digested
food
iii. produces hormones that affect the activity of the
digestive system
d.
changes along the tubular tract: in the esophagus there’s
stratified squamous as needed in an area where lots of
protection from abrasion is needed. In the stomach, the
lining changes to simple columnar.
e.
Epithelial lining form glands that leave the epithelium and
go to the:
i.
lamina propria
ii. submucosa
GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 2 of 8
D.
E.
F.
iii. outside the gastrointestinal tract
f.
Epithelial lining may be thrown into folds or villi in effort to
incr the surface area for absorption
2. lamina propria contains:
a.
Glands
b.
lymphatic tissue (nodules and diffuse lymph)
c.
macrophages which help protect from infection
3. muscularis mucosa (not externa, which is another layer) consists of 2
thin layers of smooth muscle
a.
inner circular
b.
outer longitudinal --promotes movement of the mucosa
independent of other movements of the digestive tract,
increasing its contact with the food.
c.
Muscularis mucosa has “localized contraction”
Submucosa
1.
“below the mucosa”
2.
The submucosa serves to connect the mucous membrane to the
muscularis externa.
3.
It consists of dense connective tissue.
4.
contains larger vessels
5.
It contains submucosal plexus of Meissner.
6.
The submucosa may have glands that originated in the mucosa
7.
has sympathetic innervations
Muscularis Externa.
1.
consists of 2 substantial layers of smooth muscle.
a. inner circular layer
b. outer longitudinal layer
2.
It may have a myenteric plexus of Auerbach and is found
between the 2 layers
3.
size of layer varies depending on where you are in the digestive
tract
Serosa or adventitia
1.
esophagus has adventitia
a. connected by connective tissue fibers
b. If connective tissue of a particular segment of the digestive
tract merges with connective tissue of surrounding structures it
is called an adventitia
2.
small intestine has serosa
GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 3 of 8
a. The serosa consists of loose connective tissue, which is
covered by a single layer of mesothelium (simple squamous
epithelium).
a. Serosa is present on parts of the tract that are surrounded by the
peritoneum
III.
Esophagus
A.
Introduction.
1.
The esophagus is a straight tube about 20 cm (8 inches) long which
extends from the pharynx to the stomach
2.
The esophagus consists of 4 layers.
3.
Food passes very rapidly through the esophagus.
B.
Mucosa.
1.
thrown into longitudinal folds that expand as a bolus of food
passes
2.
Epithelium: The esophagus is lined by a non-keratinized, stratified
squamous epithelium, which undergoes continual renewal
3.
The muscularis mucosa is thickest in the esophagus, consisting of
~ 20 layers.
C.
Submucosa
1.
In the submucosa, the fibroconnective tissue contains coarse
collagenous and elastic fibers.
2.
The submucosa is also thrown into folds which expands as food
passes.
3.
also can contain exocrine glands (further discussed later in this
scribe)
D.
Muscularis Externa.
1.
The upper 1/3 contains skeletal muscle associated with pharynx.
2.
The middle 1/3 contains both skeletal and smooth muscle.
3.
The lower 1/3 consists of only smooth muscle.
C.
Clinical Correlation – Barrett esophagus; reflux wears away the
stratified squamous epithelium and causes ulcers in regions of the
esophagus.
1. after erosion, metaplasia occurs: in pathological terms that means a
normal epithelial layer is replaced by another normal epithelial layer.
a. The strat squam epi is relaced by simple columnar, mucous
producing epi which is able to withstand the acidic
environment;
b. this is NOT cancer since it’s replaced by something that’s
normal and not cells that grow uncontrollably.
GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 4 of 8
F.
IV.
c. embryologically, the esophagus is simple columnar at first
d. mucous is produced because it serves a protective role.
Glands.
1.
A few mucous glands are scattered in the submucosa and are called
esophageal glands (mucus secretion).
2.
they stain homogeneously and look like mucosal cells on histo
slides
3.
esophageal cardiac glands are mucous glands near the stomach in
the lamina propria.
4.
note that cardiac glands are in the stomach and esophagus and you
must know which one you’re talking about; thus there are
esophageal and gastric cardiac glands.
5.
be able to recognize these cells on slides (the white “frothy” cells)
Stomach
A.
Introduction.
1.
The stomach is a dilated segment of the digestive tract that acts as
a reservoir for ingested food, which is termed chyme (the stomach
contents).
2.
The presence of HCl restricts bacterial growth within the stomach.
3.
Clinical Correlation: Cells in the stomach are the source of
intrinsic factor
a. needed for absorption of vit B12;
b. deficiency leads to pernicious anemia because can’t make
RBC
4.
has 4 layers as in other parts of the digestive tract: mucosa, sub~
and muscularis externa and serosa
5.
Some absorption will occur in the stomach (e.g. alcohol, H20).
6.
composed of four regions:
a. cardiac - level of esophagus entry to stomach
b. fundus – “the hill”
c. body
d. pylorus - the end of the stomach just before entering the small
intestines.
7.
Rugae are folds, which greatly increase the surface area of the
stomach. Allows for large expansion and absorption. Absent in the
distended stomach.
B.
Mucosa
1.
Large in the stomach compared to the esophagus
GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 5 of 8
2.
C.
D.
Epithelium: there is a very delineated, drastic change at the
esoph/stomach junction from strat squamous to simple columnar
a. Surface epithelial layer consists of tall, simple columnar, which
are replaced every 4-7 days.
b. Cells die via apoptosis and are sloughed off at the luminal
surface.
c. Have nuclei located at the base of the cell
d. Mucin production provides a protective coating over this
epithelium.
3.
Lamina Propria:
a. Gastric glands form as invaginations. These glands are simple
branched tubular glands located in the lamina propria which
open via gastric pits.
b. The three types of gastric glands are cardiac, fundic and
pyloric.
c. proportionally there are LOTS of gastric glands and only a
little bit of lamina propria
4.
Muscularis Mucosa
a. Secretory exocrine gastric glands extend down to muscularis
mucosa
Cardiac Region and Cardiac Glands.
1.
The cardiac region of the stomach is a narrow circular band, only
1.5 to 3 cm wide.
2.
The lamina propria contains cardiac glands which
a.
are centered at the esophageal orifice and are simple or
branched tubular glands which extend into the deeper half
of the mucosa
b.
are generally short glands, with short pits but a longer
glandular part. Don’t extend all the way to the Muscularis
mucosa.
c.
resemble glands of the terminal region of the esophagus.
On both sides of sphincter, there is mucous production
which allows for easy flow of food to the stomach.
d.
Mucous stains brighter than the other structures on the
slide.
Fundus, Body and Fundic Glands.
1.
The fundus is a dilated region, which lies to the left and above the
cardiac orifice.
2.
The largest portion of the stomach is the body.
3.
Fundic glands are branched, tubular glands found in the lamina
propria and make up greater than 99% of stomach glands.
GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 6 of 8
4.
5.
a.
b.
c.
d.
e.
These glands are the main acid, enzyme and endocrine
producing glands in the stomach.
Six different cell types are found in the fundic gland.
Surface epithelial cells
i. produce a basic mucous, which serves a protective role.
Undifferentiated or stem cells
i. have a capacity to undergo mitosis and replace cells of the
glands such as parietal, enteroendocrine and chief cells.
ii. found in the neck region.
iii. Some migrate up toward the lumen and replace surface
mucous cells, which have a turnover rate of 4-7 days.
Chief cells
i. basophilic cells
ii. found in the lower region of the tubular gland.
iii. produce enzymes such as lipase (for triglyceride
breakdown) and pepsinogen (“pro” forms), which is
converted to pepsin in the acidic environment of the
stomach.
iv. have apical granules.
Parietal cells
i. found at the upper region of the gastric gland, but are
scarce at the base.
ii. pyramidal or round
iii. central nucleus and eosinophilic cytoplasm
iv. have numerous mitochondria and deep invaginations of
apical membrane forming canaliculi, indicating there’s a lot
of movement across the surface.
v. When inactive, parietal cells have tubulovesicles at their
apical region
vi. when stimulated to produce HCl, these vesicles fuse with
the cell membrane to form microvilli, which increases the
surface area
vii. These cells are the source of HCI and gastric intrinsic
factor (essential for vitamin B12 absorption and proper
RBC production).
Mucous neck cells
i. found between parietal cells in the neck of gastric glands
ii. produce a mucopolysaccharide that is different from the
surface epithelial cells: protects the stomach from acidic
environment.
GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 7 of 8
E.
F.
iii. irregular in shape
iv. nuclei at their base
v. They are also where mitotic activity occurs which is
indicative of bidirectional flow: undiff cells can go up to
the lumen or down to the muscularis mucosa. Having
mitotically active undifferentiated cells integrated
throughout allows for reformation of the stomach every 4
days
f. Enteroendocrine cells
i. located at the base of glands
ii. have basal granules suggesting an endocrine function.
1. Compared to exocrine cell, the granules are located
at the base; the product must go into the
vasculature. Thus the granules are near the lamina
(Connective tissue)
iii. produce gastrin and histamine.
iv. can see with silver stain.
b. When looking at histo slides and you see many glands but
little/scarce connective tissue, you know you’re in the region of the
stomach. The glands stretch far down through the mucosa.
c. note that the parietal and chief cells are eosinophilic (reddish)
g. enzymatic producing cells are at the base and have to work their
secretions all the way up to the surface of the stomach
h. the chief cell is a protein/enzyme producing cell
i. know where you would find each of the cells (apical region or
basal region)
Pylorus and Pyloric Glands.
1.
The body of the stomach continues into a region called the pyloric
antrum, which narrows to the pyloric canal, which further narrows
to the pylorus.
2.
The pylorus has deep gastric pits into which the branched tubular
pyloric glands open. Therefore these glands are relatively short and
similar to those in the cardiac region.
3.
Pyloric glands have primarily mucous producing cells.
4.
Scattered enteroendocrine cells are present; very few though
5.
there are mucous prod cells at the beginning and end of the
stomach: Allows for food (chyme) to move easily in and out of the
stomach
Lamina Propria.
1.
The lamina propria is scanty consisting of collagenous and
reticular fibers.
GI #10
Tue 2/18/03 11am
Dr. Wordinger
M. Shiller
Proscribe Samera Kasim
Page 8 of 8
G.
H.
I.
J.
2.
It is more obvious in cardiac and pyloric regions.
3.
It is occupied by lymphocytes, mast cells and plasma cells.
Muscularis Mucosa
1.
The muscular mucosa is not extensive.
2.
It has slips of smooth muscle extending into the lamina propria
between gastric glands.
Submucosa
1.
The submucosa consists of dense connective tissue and collagen,
reticular and elastic fibers.
2.
It contains the submucosal plexus of Meissner.
3.
The submucosa contains blood vessels, lymph vessels and nerves.
4.
It has macrophages, mast cells and lymphoid cells.
Muscularis Externa.
1.
The muscular externa has three (3) layers of smooth muscle.
This is very unique the to pyloris region
a. The 3rd layer, the oblique layer, allows for churning and true
mixing of food necessary to digest food.
2.
These layers are an outer longitudinal, middle circular and inner
oblique muscle layer.
3.
The myenteric plexus of Auerbach is found between the circular
and longitudinal layers.
4.
Its major function is to affect the mixing action of the stomach
Serosa.
1.
The serosa consists of a layer of loose areolar connective tissue
covered by a mesothelium.
2.
It has blood vessels and nerves.