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Reptiles NOT Anaerobic



Date: Mon, 6 Jan 1997 22:19:34 -0500
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To: mrowe@indiana.edu, cnedin@geology.adelaide.edu.au
Subject: Reptiles NOT Anaerobic
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From: DOrr131386@aol.com
Subject: Reptiles NOT Anaerobic

There seems to be a *rumor* afoot within the paleontology community that
reptiles rely
primarily on anaerobic metabolism for muscular activity.


The direct source of energy for intracellular processes, in all known
living cells, is the
conversion of adenosine triphosphate (ATP) to adenosine diphosphate (ADP).
This powers cell division, protein synthesis, nerve impulses and muscular
contraction,
among others.  During anaerobic glycolysis each sugar molecule metabolized
results in the production of 2 molecules of ATP.  This is sufficient for
may functions but is not enough for energy intensive processes such as
muscular contraction.


Eukaryotic cells generally contain mitochondria, within which the pyruvate
by-product of glycolysis is processed aerobically via the citric acid cycle
and oxidative phosphorilization. This brings the total ATP produced to 24
molecules!  This is the primary energy cycle in eukaryotes, including all
plants, fungi and animals.  Analogous processes occur in most bacteria.
Mitochondria are especially abundant in high energy cells such as muscular
cells in animals.


The limiting factor in this process is primarily the availability of
oxygen.  The typical reptilian 3 chambered heart passes only part of the
blood through the pulmonary circulation during passage through the heart.
As a consequence reptilian blood tends
to be poorly oxygenated.  This is okay for them, itís all the oxygen they need.


Endotherms have more efficient means of supplying oxygen for muscular
contraction.  Mammals,  for example, have a diaphragm muscle to assist in
respiration and a 4 chambered heart to provide more fully oxygenated blood.
Birds top this with lungs that function like gas diffusion towers, running
the blood flow and the air flow continuously in opposite directions.


The generation of the majority of the body heat in endotherms is not a
result of aerobic metabolism (which also occurs in ectotherms) but is,
instead, a result of muscular contraction.  Four times as much energy is
dissipated as heat during muscular contraction
than is produced as actual ìworkî.  Even at rest a mammalís skeletal
muscles are in a state of constant activity.  As the surroundings become
colder, this increases, eventually becoming quite apparent as shivering.


Maintaining an erect posture, even a quadrapedal one, also requires
constant muscular activity.  Any animal assuming a more or less permanent
erect posture becomes an endotherm whether it wants to or not, including
dinosaurs !!!


Douglas Orr




cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
-------------------------------------------------------------------
Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.