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Re: Ruben was right
I don't understand this argument (note that I don't claim it is wrong,
I just don't understand it): The metabolising happens inside the
body. How much of its end-products end up in the exhaled air depends
on how permeable the lung tissue is to the substances, doesn't it?
Water molecules are identical. It does not change anything if water that
evaporates in lungs is metabolically produced or was taken from somewhere
My analysis was simple bookkeeping exercise. It counts what comes in and
what comes out.
Imagine the blood-air-barrier were completely impenetrable to water,
then there would be no water exhaled. Imagine it were completely
impenetrable to CO2, there would be no CO2 exhaled. So is it clear
that partial pressures must be the same?
BTW, these are questions that could be easily answered by
experiment. Here's an abstract I found with google:
No. Any experiment deals with more than one hypothesis but with multiple.
Care must be taken.
The both abstracts you have posted do not state CO2 pressure in exhausted
air and body temperatureof animals. That makes is slightly incomplete.
At 35ÂC, hovering (not resting!) hummingbirds apparently face the danger
of overheating. As they do not have sweat glands, they _have to_
hyperventilate their lungs. (CO2 pressure should decrease)
And... Hummindbirds feed mostly on flower nectar. Read what I've wrote about
generic animal feeding on glucose. As long as humminbirds have body T<53ÂC,
that goes well with my analysis.
At 0 Â C the respiratory water loss and metabolic water production were
If hummingbirds were endotherms that would disprove my analysis.
But I was reffering to lung temperature, not ambient air temperature.
In my generic 4%CO2 animal model, that could be interpreted as: at ambient
T=0ÂC the bird has
body T of about 41ÂC and lung T about 29ÂC, and does not hyperventilate its
lungs (does not need to). Do you disagree that hummingbirds are endotherms?
Good you haven't brought an example of perpetuum mobile.
Respiratory metabolism and evaporative water loss in a small tropical
lizard Oxygen consumption (VO2 ) and evaporative water loss were
determined in the 0.45-g mesophilic lizard,Sphaerodactylus macrolepis,
similar to oxygen consumption. At 30ÂC, total evaporative water loss
was 5.4 mg H2O gâ1 hâ1. Nonrespiratory evaporative water loss was 5.1
mg H2O gâ1 hâ1 and accounted for 94% of total evaporative water
Whereas water loss is 5.4mg which is 30 times larger (the difference
Again you compare wrong values... My generic animal model does not predict
nonrespiratory water losses (the goal was to testify Ruben's claim).
And in the second abstract we do not know respiratory water loss.
We could substract 5.1 from 5.4 but result is highly unreliable as both
numbers are approximate and we get what is "Loss of precision in
(Please don't ask me to tell about metrology and ariphmetic. -> Google)
This does not contribute to Ruben's claim that ectotherms do not have to
worry about respiratory water loss. Rather reverse.
Also, I would not be surprised if it someone showed that resting
ectotherms have exhausted air with CO2<4%.
gets bigger if you convert to mols). So it seems not to be true that
for each molecule of O2 consumed (and thus for each molecule of CO2
exhaled) there is exactly one molecule of O2 exhaled as well.
Well known, and easily deduced from chemical formulae.
CO2/O2 metabolic process
<1 protein dissimilation
<1 fat dissimilation
=1 carbohydrates dissimilation
1 fat synthesis from carbohydrates
Or did I miss something (again)?
Yes. You read amazingly fast.
I used 'assimilation' where should be 'dissimilation' in previous post.