Re: Brains size and sweat

Bill Frix (
Wed, 8 Jan 1997 15:11:16 GMT-5

To respond to Jonathan Arm's message of Wed, 8 Jan 1997 14:28:09:

> In response to some of the stuff on sweat, we seem to be
> ingoring the importance of the circulation in aiding
> evaporative heat loss. I am a little rusty on some of the
> physiology here, but when we are hot we not only sweat, but
> vasodilate in order to aid in the conduction of heat from
> its source to the site of heat loss - i.e. the skin. It may
> not make a whole lot of difference where the heat is
> generated as long as the circulation is efficient.

According to the books of physiology and anatomy I read today, in
humans, vasodilation accounts for 60% of heat loss while persperation
accounts for 25%.

> As for dessert animals, they need to conserve water, and
> have superbly efficient kidneys with extra long and
> efficient loops of Henle to concentrate the urine. They
> would not be expected loose too much water through sweating
> but would have to find other methods of cooling - can anyone
> tell us what?

According to the texts, many desert creatures use radiation and
estivation like behavior to regulate their body temperature. We have
seen the enlarged ears on the jack-rabbit, as opposed to the
cottontail. These are the heat radiators used by the desert dwelling
jack. Desert dwellers also tend to burrow and seek shade (the origin
of the siesta; a very important and reasonable concept I learned
while living in Phoenix, Arizona). Their body metabolisms reduce to
lower the amount of energy production (try fasting on a hot day - you
_will_ feel cooler).

William M. Frix
Assistant Professor, Electrical Engineering
Box 3021
John Brown University
Siloam Springs, AR 72761
Phone: (501) 524-7466
FAX: (501) 524-7499