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Re: CO2



At 05:43 PM 8/7/01 -0400, Richard Bowman wrote:
CO2 in solution is carbonic acid. This can make blood acidic, but that is
why our bodies have a buffering systems to control this.

True, but there's more to the story:
-- Yes, buffering controls the pH and CO2 in the short run.
-- Breathing controls the CO2 levels in the longer run.
-- The kidneys (and intestines, to some extent) control the pH in the
long run. (Obviously you can't exhale H+ ions.)

CO2 and H2O are the major products of the metabolism of glucose, the sugar
that all carbohydrates, ...

Right.

... the sugar that all carbohydrates, proteins and fats are changed into
in their metabolic degradation.

Really? I thought fats were metabolized via their own system, without any
need for a glucose intermediary.
http://web.indstate.edu/thcme/mwking/fatty-acid-oxidation.html

Thus CO2 is present through the tissues of our bodies so that
worrying about having some extra for a brief time in our stomachs seems
too weird to really comment on.

Indeed.

To put this in perspective, let's run the numbers for a 12-ounce can of
soda (not diet soda). I figure it's got about 3 atmospheres of CO2.
0.375 liter x 3 Atm --> 1.1 liter STP --> 0.05 mole of CO2
Now, that same can of soda has about 40 grams of carbohydrate. That's
4/3rds of a mole of CH2O. In other words, metabolizing the sweetener puts
at least 25 times more load on the CO2 disposal system than the carbonation
does.

==================

A few more facts... Occasionally useful... Not as widely known as they
should be:

-- The length of time you can hold your breath does not typically have
much to do with running out of oxygen. Rather, it has to do with
overloading on CO2. This is not super-obvious to most people, because under
most conditions, anything that produces CO2 consumes oxygen, so it's not
easy to distinguish one process from the other. Can you design a
non-hazardous experiment to test this?

-- This has interesting implications for diving mammals (whales, seals,
humans) and for spacefarers. It doesn't do you much good to carry lots of
oxygen if you haven't got a good way to deal with the CO2.
http://www.nwdesigns.com/rebreathers/rbfaq.htm

-- People are very sensitive to their internal CO2 levels. This directly
drives the urge to breathe. Can you design a non-hazardous experiment to
test this?

-- In contrast, people exhibit remarkably little direct sensitivity to
oxygen levels. The reaction to mild hypoxia varies from person to
person. Usually people get drowsy. There may be a feeling of euphoria
(happy drunk) or the opposite (pugnacious drunk). Physical strength is
impaired. Vision is impaired. Conspicuously lacking is any innate sense
that you're not getting enough "air".

-- Over a period of days, the body responds to mild hypoxia by producing
more red blood cells.