Download pyloric sphincter - Medico Tutorials

STOMACH
Dr IramTassaduq
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STOMACH

The stomach
functions both as a
reservoir and as a
digestive organ. It
empties its contents
in small portions
(suitable for
continued digestion)
into the small
intestine
Anatomically, the stomach is divided
into




cardiac part,
fundus,
body
pyloric part
(pyloric antrum
and pyloric canal)
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CARDIAC SPHINCTER

The cardiac sphincter
is a specialized valve
found between the
esophagus and the
stomach. It prevents
backflow of food and
digestive enzymes.
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FUNDUS

The is the frontal
region of the
stomach. It begins
digestion of
proteins and mixes
together stomach
contents.
BODY

The body is the
central region
of the stomach.
It also digests
proteins and
blends
materials found
in stomach.
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PYLORUS and PYLORIC
SPHINCTER


The pylorus is the back
region of the stomach. It
contracts to empty materials
from the stomach into the
small intestine
The pyloric sphincter is a
specialized valve that
prevents materials and
digestive enzymes from
escaping into the small
intestine before digestion is
completed in the stomach.
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RUGAE LINING OF THE
STOMACH

Rugae are
found on the
interior layer of
the stomach
and aid in
breaking down
food when the
stomach
contracts.
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Gastric areas (mammillated
areas).
Mucosa is divided by furrows
into small irregular elevations.
These are the gastric areas.

Gastric pits (foveolae).
surface of each gastric area to
be studded with minute
depressions, the gastric pits.

Mucosa.
Epithelium

Simple columnar
 Lamina Propria
contains glands which
differ in each
histological region of
the stomach.
 Muscularis
Mucosae.
It measures from 0.31.5 mm in thickness,
being thinnest in the
cardia and thickest in
the body and fundus.
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SUBMUCOSA


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This layer separates
the muscularis from
the mucosa .
It consists of coarse
collagenous fibers and
many elastic fibers,
plus blood vessels,
lymph vessels, nerves,
and the plexus of
Meissner. Glands are
absent.
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MUSCULARIS EXTERNA



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an outer longitudinal,
a middle circular,
and an inner oblique.
The oblique layer is best developed in the cardia and
body. The circular layer is thickest in the pylorus
where it forms the pyloric sphincter, which helps
control the evacuation of food. The longitudinal layer is
continuous with the longitudinal muscle layer of the
esophagus and duodenum. The myenteric plexus
lies in the connective tissue lamina, which separates
the circular from the longitudinal muscle fibers.
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SEROSA

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The outer layer
consists of loose
connective tissue
covered on its
superficial aspect by
mesothelium. Small
blood vessels,
lymphatics, and
nerves lie in the
connective tissue.
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SURFACE EPITHELIUM



surface epithelium (simple, tall
columnar).
It contains mucus-producing
cells, surface mucous cells,
The mucus is alkaline and
adheres to the epithelium.
which protects the mucosa
from the acidic contents of the
stomach.
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GASTRIC GLANDS
 cellular
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composition
and function of
the gastric
glands are
specialized in
the different
parts of the
stomach
GASTRIC GLANDS
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- Secrete mucus to protect
epithelial cells from enzymes
& acid
- Secrete HCl (for protein
digestion) & intrinsic factor (for
B12 absorption)
- Secrete pepsinogen which
gets converted to “pepsin”
when mixed with HCl; for
protein digestion
Entero-
- Secrete gastrin to regulate
stomach emtying
CARDIAC GLANDS



Cardiac glands are
heavily branched
tubular glands
which contain
mainly mucusproducing cells.
Shallow Gastric Pits
Short glands
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PRINCIPAL or FUNDIC GLANDS
Each glandular
tubule consists
of three parts:
 deep body,
 intermediary
neck
 upper isthmus.

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PYLORIC GLANDS

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Branched, coiled
tubular glands.
Endocrine cells, in
particular gastrinproducing cells, are
more frequent than in
principal glands. A few
parietal cells may be
present but chief cells
are usually absent.
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In the pylorus, the
pits extend
downward to about
one-half the
thickness of the
mucosa;
 in the cardia, and
fundus, the pits
occupy only onefourth the thickness
of the mucosa

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MUCUS NECK CELLS

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are found between
the parietal cells in
the neck of the
gland.
They are difficult to
distinguish from chief
cells in plain H&E
stained section
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Chief cells (or zymogenic cells)


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contain Zymogens
granules
Abundant RER give
the cell Basophilic
stain
most numerous of
the four types. They
occur primarily in the
body of the glands.
produce pepsinogen,
which is a precursor
of the proteolytic
enzyme pepsin.
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Parietal cells (or oxyntic cells)


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Large acidophilic
cells.
secrete the hydrochloric
acid of the gastric juice.
Aside from activating the
pepsinogen
Parietal cell also secrete
intrinsic factor, which is
necessary for the
resorption of vitamin B12
On electron microscopy reveal
Intracellular canalicular system
and Tubulovesicular System
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ENTEROENDOCRINE CELLS

Scattered between the
epithelial cells of the
gastric mucosa and their
basement membrane.

Demonstrated by Electron
microscope or by
Immunological
technique.On light
microscopy they appear
clear.

Secretion is released in the
lamina propria and
distributed by blood
vessels.
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Endocrine cells


The best characterized endocrine cells in the
gastric mucosa are gastrin-producing cells (G
cells) and somatostatin-producing cells (D cells).
G cells are most frequent in the middle third of
the glands. They stimulate the secretion of acid
and pepsinogen. G cell function is stimulated by
nervous input, the distension of the stomach.
D cells are found mainly in glands of the pyloric
antrum. They inhibit G cells and thereby acid
production. D cell function is stimulated by acid in
the lumen of the stomach and duodenum.
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Cell renewal


The surface epithelium is
renewed approximately
every third day.
The source of the new
cells is the isthmus, i.e.
the upper part of the
neck, of the gastric
glands, where cells divide
and then migrate towards
the surface epithelium
and differentiate into
mature epithelial cells
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