EVACUATION OF GASES FROM GASTROINTESTINAL TRACT
Normally, gas
accumulates in the GI tract either because of entrance of outside air or
production of gases in the body. Accordingly, the gases accumulated in GI tract
are classified into two groups:
1. Exogenous gases
2. Endogenous gases.
Exogenous Gases
Exogenous gases form about
90% of accumulated gases. These gases enter the GI tract either by swallowing through
mouth or drinking carbonated beverages.
2. Endogenous Gases
Endogenous gases form
about 10% of accumulated gases. These gases are produced by digestion of food stuffs
and interaction between bacteria and food stuffs in the intestine.
EVACUATION OF
ACCUMULATED GASES
Evacuation of accumulated
gases usually occurs by two processes:
1. Belching
2. Flatulence.
BELCHING
Belching is the process
by which the gas accumulated in stomach is expelled through mouth. It is also
called burping.
It occurs because of inflation (distention) of stomach by swallowed
air. The distention of the stomach causes abdominal discomfort and the belching
expels the air and relieves the discomfort.
Most of the gas accumulated
in stomach is expelled through mouth. Only a small amount enters the intestine.
Causes for Accumulation of Gases in Stomach
1. Aerophagia:
Swallowing large amounts of air due to gulping the food or drink too rapidly
2. Drinking carbonated
beverages
3. During some
emotional conditions like anxiety lot of air enters the stomach through mouth.
Act of Belching
Belching is not a
simple act and it requires the coordination of several activities such as:
1. Closure of larynx,
which prevents entry of liquid or food with the air from stomach into the
lungs.
2. Elevation of larynx
and relaxation of upper esophageal sphincter. It allows exit of air through
esophagus more easily.
3. Opening of lower
esophageal sphincter.
4. Descent of diaphragm,
which increases abdominal pressure and decreases intrathoracic pressure.
All these activities
are responsible for the expulsion of air from stomach to the exterior via
esophagus.
FLATULENCE
Flatulence is the
production of a mixture of intestinal gases. The mixture of gases is known as flatus
(in
Latin, flatus = wind).
Expulsion of flatus through anus under pressure is called farting or passing
gas. Farting is associated with disagreeable odor (due to odorous gases) and
sound (due to vibration of anal sphincter).
Quantity of Flatus
Average flatus released
by human is about 500 to 1500 mL per day, with 10 to 25 episodes throughout the
day.
Source of Gases in Intestine
Flatulence is the
mixture of gases present in the intestine. Flatulence by swallowed air is rare.
Common sources of
gases in flatulence are:
1. Bacterial action on
undigested sugars and polysaccharides (e.g. starch, cellulose)
2. Digestion of some
flatulence producing food stuffs such as cheese, yeast in bread, oats, onion,
beans,
cabbage, milk, etc.
Constituents of Flatus
Major constituents of
flatus:
1. Swallowed
non-odorous gases
i. Nitrogen (major
constituent)
ii. Oxygen
2. Non-odorous gases
produced by microbes
i. Methane
ii. Carbon dioxide
iii. Hydrogen
3. Odorous materials
such as
i. Low molecular weight
fatty acids like butyric acid
ii. Reduced sulfur
compounds (hydrogen sulfide and carbonyl sulfide).
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