FOR IMMEDIATE RELEASE
December 17, 2007
APS Contact
Christine Guilfoy
Office: (301) 634-7253
cguilfoy@the-aps.org
www.The-APS.org
Help Santa Stand Up to the
Heat Physiologists Offer Santa Some Tips for a Cool Ride
BETHESDA, Md. − Santa Claus is well adapted to
living in the subzero temperatures of the North Pole: He has a good supply
of insulating fat and his plump physique and ample facial hair reduce the
surface area exposed to the elements. Additionally, Santa’s fashionable and
widely-imitated attire would meet the cold-weather quality control
specifications of your mother.
All these things help Santa adapt to the cold, but how
will Santa cope with the heat when he travels to hot climates with his
sleigh full of toys? Luckily, physiologists can help Santa resolve this
problem.
Lisa R. Leon is a physiologist at the U.S. Army
Research Institute of Environmental Medicine in Natick, Massachusetts. When
not thinking about Santa, she investigates how the body maintains its “set
point” of 98.6° F, under widely varying environmental temperatures,
particularly in extreme heat. Specifically, Leon studies what happens at the
molecular and cellular levels to provoke the physiological changes that
protect us from overheating (hyperthermia).
Advice to Santa: Be Cool
Leon knows what Santa should do first: remove his
jacket and hat, take off his boots and dangle his bare feet over the sled as
he flies toward Miami. In doing so, he will expose greater body
surface areas to the air. The more surface area exposed, the greater the
loss of heat, which is why we curl up when we want to stay warm and stretch
out when we want to cool down. Similarly, mice like to expose their furless
tails, feet, noses and ears to help dissipate heat.
How does this work, from a physiological perspective?
Leon says the body’s surface blood vessels open up (vasodilate) when the
core temperature rises beyond its set point. At the same time, the internal
core blood vessels constrict, shunting the warmer blood from inside the body
to the skin, where the cooler surface air draws away heat from the blood.
Behavioral changes, such as removing a coat, are the
first line of defense to ward off overheating. Behavioral changes that keep
us cool are usually easy to make and they have an advantage. When the body
must cope with the heat by using physiological processes such as sweating,
there is always the risk of exhausting the response and suffering heat
stroke as a result.
Do sweat it
Even after Santa removes his jacket, his primary
physiological response to heat, sweating, is likely to begin. Sweat,
comprised of water and electrolytes such as salt, is a great conductor of
heat and cold. That’s why sweat is less effective in humid climates, where
it evaporates more slowly, or not at all. (Under really high humidity, the
sweat will simply roll off the skin and not help to cool.) It is also why
submersion in cold water cools the body down much faster than air of the
same temperature and explains why Santa hardly ever goes swimming in the
North Pole winter.
When the blood vessels dilate and move the warm blood
to the skin surface, the sweat picks up the heat, which is then removed from
the body as the sweat evaporates. Some animals that don’t sweat, such as
mice, lick their fur to cool down. As the saliva evaporates from their fur,
it also whisks away heat.
Santa’s reindeer will take a slightly different
approach. They will open their mouths, dangle their tongues and pant when
they get hot, thus exposing greater surface area to the air and using
evaporation to draw away heat from their bodies, says Perry S. Barboza, who
studies reindeer at the Institute of Arctic Biology at the University of
Alaska in Fairbanks. So, please understand that those panting sounds from
Rudolf and his gang on the roofs in the warmer climates are unavoidable.
What to Leave Out for
Santa and His Reindeer?
When the body resorts to physiological changes to
maintain normal temperature, there is the risk that physiological responses
will eventually break down. For example, sweating can lead to significant
fluid loss, which can draw water from the blood cells, resulting in thicker
blood that creates a strain on heart.
So give Santa a break: Residents of cold climates may
offer pie and cookies, which will speed up his metabolism and help keep him
warm. They might also leave some liquid refreshments, because the cold can
evaporate moisture out the body. Residents of warmer climates should leave
plenty of water or sport drinks, including a generous array of various
liquid refreshments on the roof.
Editor’s Notes: An audio version of this story
will appear on Life Lines, the podcast of The American Physiological
Society. You can find it at
www.lifelines.tv on
December 14.
To arrange an interview with Dr. Lisa Leon about any
aspect of temperature regulation in the heat or cold, or with Dr. Perry
Barboza to find out more about reindeer, please contact Christine Guilfoy at
cguilfoy@the-aps.org or (301) 634-7253.
Physiology
is the study of how molecules, cells, tissues and organs function to create
health or disease. The American Physiological Society (APS) has been an
integral part of this scientific discovery process since it was established
in 1887.
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