This is an interesting question! Gas is formed in
our bodies from food, drink, and ingested air. Gas
can be released from the body in a couple of ways:
either through the mouth through burping,
or out the rectum via flatulence.
With regard to burping: our stomachs will
sometimes contain excess gas (from air that has
been swallowed or from digesting food which
contributes to excess gas -- e.g. carbonated
beverages). The excess gas in our stomach
builds pressure against the lower esophageal
sphincter (located at the base of our
diaphragm and at the top of the stomach).
Eventually, as the pressure builds up enough, air
will be released into the esophagus, and when
enough pressure builds up against the upper
esophageal sphincter (at the back of the throat),
air is released there as well.
The gas formed in our intestines which is
eventually destined to be expelled as flatulence
is a very low density mixture of various
chemical compounds, ranging from nitrogen and
carbon dioxide to various molecular compounds that
are byproducts of the bacterial fermentation that
our food and drink undergo during digestion.
There are a couple of things we need to think
about when trying to determine if this gas can be
absorbed by the body. The first surrounds
molecular considerations: how soluble a certain
gaseous compound is in solution. When we talk
about solubility, we talk about the ability
of a solute to dissolve in a solvent (solute +
solvent = solution).
Various factors affect solubility, such
as temperature, how similar the polarities of
solvent and solute molecules are, pH, pressure,
and molecular size. How much solute actually
exists in a solution can also be affected by
equilibrium balances and extent of reaction (you
can read more about this by looking up Le
Chatlier's principle ). And even then,
sometimes, especially in living organisms,
chemicals can move up their concentration gradient
with the help of enzymes or other auxiliary
While the compounds comprising intestinal gas
could theoretically be absorbed into the body to
some extent (they might be somewhat soluble in our
bodily fluids), they do end up being expelled. To
a large extent, this is driven by the fact that
these byproducts are considered waste and not
really usable by the body.
However, that is not to say that there is not
a large amount of gas that is actually held by the
body. For instance, carbon dioxide we breathe in
(air we breathe has a mixture of gases!) forms
bicarbonate in the body and also can combine with
hemoglobin. These processes contribute to the
solubilization of carbon dioxide relative to how
much could normally be held in a simple solution.
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