[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Re: Reptiles NOT anaerobic
Sorry, folks, I deleted this message from Douglas Orr before saving any
of it electronically for a response, so I can't regurgitate much of the
Orr is right in asserting that living reptiles would rather be aerobic
than anaerobic. And the problem is, indeed, that their cardiopulmonary
system is inadequate to supply oxygen at a high enough rate to fuel high
levels of muscular contraction.
However, that is just the problem. Reptiles can do fine using aerobic
metabolism when lying around on their bellies. When they have to do
something that requires exertion, the need for ATP quickly exceeds their
ability to produce it, and they switch to anaerobic metabolism to make up
the shortfall. Anaerobic metabolism produces lactic acid as a
by-product. The rapid build-up of lactic acid results in the feeling of
fatigue (I presume reptiles would feel it--humans can) and loss of
ability for muscular contraction. That's why reptiles can't run very
far. That's also why very large animals like dinosaurs, which must have
expended large amounts of energy just walking around, probably had
cardiopulmonary systems adequate to supply enough oxygen to fuel elevated
rates of aerobic metabolism. Whether those elevated rates reached
anything near to what mammals and birds do is another matter.
Even endotherms switch to anaerobic metabolism when they have a sudden
need for a large amount of energy. Joggers can run all day when they
stay "within themselves," but sprinters cannot sprint very far because
they exceed their aerobic limit, switching to anaerobic metabolism and
becoming fatigued the same way lizards may when they are merely walking
The statement "The generation of the majority of body heat in
endotherms is not a result of aerobic metabolism (which also occurs in
ectotherms) but is, instead, a result of muscular contraction" (that
is an accurate quote from Orr's posting) may be misleading. Aerobic
metabolism is only about 40% efficient. The other 60% of energy
generated is given off as waste heat.
Thus, even when animals are totally inactive, they are producing body
heat. My point is to emphasize that aerobic metabolism DOES produce
excess heat that contributes to the elevated temperatures of endotherms.
However, Orr may be right in asserting that this is a minority of the
heat that endotherms produce, and that ectotherms produce body heat the
same way--he seems to know the numbers better than I.
But it is not just a rumor that living reptiles rely primarily on
anaerobic metabolism for muscular activity. As noted above, they RELY on
anaerobic metabolism for doing anything except just sitting there, or
perhaps leisurely feeding or casually slithering down to a water hole.
Norman R. King tel: (812) 464-1794
Department of Geosciences fax: (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712 e-mail: firstname.lastname@example.org