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8/8/2019 Anatomy and Physiology- Stomach
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ANATOMY AND PHYSIOLOGY
Stomach
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Stomach
It is J shaped dilated portion.
Situated in the epigastric, umbilical and left
hypochondriac regions of the abdominalcavity.
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Organs associated with the
stomach Anteriorly- left lobe of liver and anterior
abdominal wall.
Posteriorly- abdominal aorta, pancreas,spleen, left kidney and adrenal gland.
Superiorly- diaphragm, esophagus and left
lobe of liver.
Inferiorly- transverse colon, small intestine.
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Cont.
To the left lateral- diaphragm and spleen.
To the right lateral- liver and duodenum
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Structure
The stomach continuous with the esophagus
at the cardiac orifice.
Continuous with the duodenum at the pyloricorifice.
It has two curvatures
- Lesser curvature- Greater curvature
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Cont.
The stomach is divided into 3 parts :- fundus,
body and pylorus.
The part of the stomach above the cardiacorifice is the fundus.
The main part is the body.
The lower part is pylorus or pyloric antrum.
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Cont.
At the end of the pyloric antrum there is
pyloric sphincter.
When stomach is inactive it is relaxed andopen.
When stomach contain food, it is closed.
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Walls of the
Consist of 4 layers:-
1. Serosa / peritoneum
2. Muscle layer3. Sub mucosa
4. Mucosa
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Peritoneum
Greater omentum
-The fold of peritoneum attaches the
stomach to the posterior abdominal wall.
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Cont.
Functions
- It stores fat which provides long term
energy- Secretes peritoneal fluid allows the organ to
glide each other .
-I
t attaches all the abdominal organs.- Isolates areas of inflammation.
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Muscle layer
It consist of 3 layers:-
1. Outer layer of longitudinal fibers.
2. Middle layer of circular fibers.3. Inner layer of oblique fibers.
This arrangement helps for churning motion
for gastric activity.
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Mucosa
The mucosa lies in large folds called rugae
The surface is a layer of non ciliated simple
columnar epithelial cells called surfacemucous cells.
There are gastric glands situated below the
surface in the mucous membrane.
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Cont.
The gastric glands contain 3 types of exocrine
cells that secrete gastric juice.
- mucous neck cells.- parietal cells.
- chief cells
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Cont.
Both surface mucous and mucous neck cells
secrete mucus.
The chief cells secrete pepsinogen (inactivegastric enzyme)
Parietal cells produces hydrochloric acid
which convert pepsinogen to pepsin.
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Cont.
Parietal cells also secrete intrinsic factor helps
in the absorption of vitamin B12.
The G cells- a fourth type of cell in the gastric glands
secrete the hormone gastrin.
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Sub mucosa
Sub mucosa of the stomach is composed of
areolar connective tissue that connects the
mucosa to the muscularis.
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Blood and nerve supply
Blood supply of stomach:
Arterial supply by branches of the celiac artery .
Venous drainage is in to the portal vein. Nerve supply:
Sympathetic supply from coeliac plexus.
Parasympathetic supply from vagus nerve.
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Gastric juice
2-3 liters secreted daily.
It consist of :
- water, mineral salts secreted by gastricgland.
- mucus secreted by goblet cells
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Cont.
Hydrochloric acid and intrinsic factor secreted
by parietal cells.
Inactive enzyme precursors (pepsinogensecreted by chief cells in the glands)
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Functions of gastric juice
Water- liquefies the food swallowed.
HCL- acidifies the food and stop the action of
salivary amylase- kills microbes
- provides acid environment for effective
digestion.
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Cont.
Pepsinogen activated to pepsin which digest
protein.
Intrinsic factor necessary for the absorptionof Vitamin B12.
Mucus prevents-
- mechanical injury to the stomach wall bylubrication.
- chemical injury by acting as a barrier.
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Secretion of gastric juice
Three phases of secretion of gastric juice :-
1. Cephalic phases
2. Gastric phases3. Intestinal phases
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Cont.
Cephalic phases
- this flow occurs before food reaches the
stomach.- and is due to reflex stimulation of the vagus
nerve initiated by smell, sight or taste of
food.
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Cont.
Gastric phases
Enteroendocrine cells secretes gastrin
Gastrin enters into the blood and stimulates
gastric gland
Produce more gastric juice
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Cont.
Intestinal phases
Partially digested contents
Reach small intestine
Hormone complex enterogastrone
Reduces gastric motility and gastric juicesecretion
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Functions of stomach
Temporary storage
Chemical digestion- pepsin converts protein
to polypeptides. Mechanical digestion- smooth muscle layers
act as a chum and mix the food and gastric
juice.
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Cont.
Limited absorption of water, alcohol and
some lipids soluble drugs.
Non specific defense againts microbes byHCL.
Dissolving out of iron from the food.
Production of intrinsic factor needed for
absorption of vitamin B12.
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Digestion and absorption
Once the food reach the stomach
The stomach wall stretched
The ph of stomach content increase
Flow of gastric juice
Initiate peristaltic movements
Chyme production
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Cont.
Gastric emptying
- each mixing wave forces a small amount of
chyme through the pyloric sphincter into theduodenum.
- food reach in CHO spend less time in the
stomach
- protein remains longer
- fat- slow gastric emptying
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Cont.
Chemical digestion begins with digestion of
protein by the enzyme pepsin.
Little absorption of water, irons and fattyacids.