Anatomy and Physiology- Stomach

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.

Anatomy and Physiology- Stomach

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