From memory, the human body sits at a fairly constant 37 degrees Celcius.
So if the ambient temperature is below 37 then the body has to generate
heat to maintain that temperature. How and where is that heat generated?
I'd presume the {*filter*} is kept warm by some organ or other, which in turn
keeps the whole body warm.

If the ambient temperature rises above 37, I expect the whole mechanism
has to turn around somewhat. All heaters off, and coolers on. Perspiration
strikes me as the likeliest coolant, and in the humidity here, it's probably
fairly poor at it's job, given that it sits on your skin and doesn't
evaporate. Does that mean that if I sat outside in 40 degree humid heat for
too long I'd expect a heat stroke?

Some interesting questions anyway ...

Ciao,

Bernd.
--

BHP Sheet and Coil Products Division, Research and Technology Centre
Port Kembla, New South Wales, Australia.

When body temperature begins to drop, respiration rate increases to
generate more heat.  The extremities have a much higher
surface-to-volume ratio, thus losing heat faster; circulation is very
important as a factor in heat distribution in this case, but not from a
particular organ.
--

                                -Daniel R. Field

When you're hot, you cool down both by sweating, and by increasing
circulation to the skin so that more heat escapes into the air.

When you're cold, you stop sweating, and you reduce circulation to
the skin so as to keep the heat inside.

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I thought I remembered temperature from a physiology outline book
I have, and sure enough, it's in the hypothalamus, which is part
of the brain stem.  The hypothalamus regulates body temperature
as well as a bunch of other things.  It controls how the endocrine
glands secrete hormones and also has some control over the
autonomic nervous system.
My book doesn't have details, but I guess the regulation of hormones
could cause us to sweat or shiver, feel thirsty, etc.
--

"The path that I have chosen now has led me to a wall....
 It rises now before me, a dark and silent barrier between
 All I am and all that I would ever want to be...."  - Livgren & Walsh

        The pathogenesis of fever is well known and the subject of
        several reviews (Dinarello 1988, Myers 1984, Hensel 1973).  The
        hypothalamus contains two areas important in temperature
        homeostasis, one located anteriorly, concerned with heat
        dissipation and containing the "hypothalamic thermostat", and a
        posterior area involved in heat generation.

        Temperature-sensitive neurons in the preoptic/anterior
        hypothalamus alter their rate of firing in response to heating
        or cooling and to input from peripheral temperature receptors.
        Injections of pyrogens here elicit fever.  Electrical
        stimulation of this area suppresses shivering and produces
        cutaneous vasodilatation, both of which lower body temperature.
        Lesions here abolish sweating in response to heat loads.

        Electrical stimulation of a second area located in the posterior
        hypothalamus produces shivering, pilo{*filter*}, peripheral
        vasoconstriction, and behaviors which raise body temperature.
        Lesions of this area prevent these activities from occurring in
        response to cold.

        When fever develops, pyrogens, primarily the endogenous pyrogen
        Interleukin 1, act on anterior hypothalamic neurons to raise the
        set point of the hypothalamic "thermostat" via a prostaglandin
        E2-mediated system.  Sensing a difference between the current
        and desired temperatures, these neurons stimulate activity in
        the posterior thalamic center to increase thermogenic
        activities.  Once body temperature has come up to the new set
        point, these activities subside.

David Nye

--
Dave Ozonoff

Boston University School of Public Health
80 East Concord St., T3C
Boston, MA 02118
(617) 638-4620