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Ralphie’s
mom was right when she bundled Randy up
for
school in A Christmas Story. However,
you can have
too
much of a good thing. By the way, they never say
what
the parents' names are in the books or the movie;
they’re
just Mother Parker and the Old Man.
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Last week we talked about ways the cold can kill you. Let’s
be a bit more upbeat today and discuss that ways your body keeps the cold from
killing you.
People tell you to wear layers of clothes when going out into the cold. Listen to them. Air is a great insulator as long it isn’t moved away from your body. Every shirt you put on traps another layer of air that can, once it’s been warmed by your body heat, keep you from losing heat to the environment.
People tell you to wear layers of clothes when going out into the cold. Listen to them. Air is a great insulator as long it isn’t moved away from your body. Every shirt you put on traps another layer of air that can, once it’s been warmed by your body heat, keep you from losing heat to the environment.
But most animals don’t wear clothes, excepting those creepy
organ grinder monkeys and the dogs and cats of little old ladies who own
knitting needles and have too much time on their hands. Do animals (including
humans) have a way to trap air without putting on layers of expensive and soon
to be out of style clothes?
Yes - it’s called hair. Hair on its own will trap air and
work to keep animals warmer in the cold, but Mother Nature has another trick up
her sleeve. You have little muscles that attach the middle of your hair
follicles to your dermal tissues. When these arrector pili muscles contract, they stand the hairs on end.
Standing hairs trap more air close to your body, so they do
a better job at insulating you from the cold. Another, less attractive, result
of this contraction is goosebumps. Yep, those little bumps are an evolutionary
mechanism meant to keep you warm.
You say, “But I get goosebumps just as often when I am
startled or creeped out as when I’m cold.” I say, “Yes, you’re right.” And the reason is because of the
way these muscles are innervated.
You (and everyone else) have two major nervous divisions to
the peripheral nervous system (everything
outside your brain and spinal cord); the somatic
nervous system and the autonomic
nervous system (ANS). The somatic system consists of sensory elements so
you know what situation your body is in (temperature, pain, touch, etc.) and
the motor nerves that let you make voluntary movements.
The ANS is involuntary. It’s rigged to automatically make
adjustments in your activities to keep you on an even keel. Things like heart
rate, pupil size, and thermoregulation are controlled by the autonomic system.
One of the automatic adjustments for thermoregulation is the contraction of the
arrector pili muscles. Think about it - you can’t make yourself have goosebumps.
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We
once had two cats – we named one Arrector and
the
other Pili. Then we had more cats, and we named
them after beers because its tough to keep
coming
up with clever names.
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Recent research hints that arrector pili muscles may be
involved in hair loss or maintenance as well. Degeneration of the arrector pili
unit can lead to fatty infiltration of the hair follicle and a choking off of
the hair growth. They don’t yet know just how this might happen so don't get too excited yet.
Since we humans don’t have much hair on our bodies anyway
(Robe Lowe’s arm hair curtain character excepted) the arrector pili mechanism
of thermoregulation doesn’t work so well for us. Good thing we have more tools
in our toolbox. If you can’t insulate your body well enough
to prevent heat loss, then you better conserve the heat you have.
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Hairy
Rob Lowe couldn’t freeze to death he tried.
He
looks like he’s wearing a sweater even
when
in the bathtub.
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Thousands of chemical reactions occur in every cell of your body every second. Most of those reactions are not 100% efficient. Some of the energy transferred is lost as heat instead of going to do work.
We spend a great deal of energy and have to eat a great deal
just to ensure that reactions produce heat and keep us relatively warm; as
mammals we are homeotherms
(misrepresented by the commonly used - warm blooded).
What can we do to make sure we lose less of this precious
heat to the cold air around us? We can bring less heat to the surface of our
body. A major amount of heat is carried in the blood, so if we keep our blood
more centrally located in our body, then less of its heat will be lost to the
environment.
We have muscles to do this as well. Constricting muscles are
located in our blood vessels and control the size of the "pipes." Make the pipe
smaller and less blood flows through it. Narrow just the pipes (vessels) near your
skin and you lose less heat to the environment. The narrowing of
the vessels is called vasoconstriction
and is the reason your skin turns pale when you are cold.
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This
is a thermal image of two hands. See how the top
one
shows cooler colors? This is what happens during
vasoconstriction
of peripheral vessels and why fingers
are
susceptible to frostbite. Why is it only one hand?
This
is a diabetic patient and they can have a localized,
exaggerated
response to cold with severe
vasoconstriction
– it’s called Raynaud's phenomenon.
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OK, your arm and leg hairs have stood on end to trap air and
you’re pale as a ghost due to vasoconstriction, but you’re still cold. We need
to make more heat!
Like we said above, the workings in your cells are far from
efficient. Muscle movements are especially good at generating extraneous heat.
That’s why you sweat while you ride your stationary bike – you know - that
thing with all the clothes hanging on it.
Shivering is a cold-induced set of micromuscular spasms
intended to generate heat without forcing you to make big movements that might
be counterproductive. It’s a pretty good way to regulate your temperature in
the cold, and research shows that it is as good as exercise in burning excess
calories.
The bad news is that babies, small children, and the elderly can’t shiver;
they haven’t developed or have lost the muscle coordination to pull it off. Babies need a
different way to generate heat. And wouldn’t you know, nature has given them
one.
We all know about baby fat, the fat that’s so hard to lose
and makes pubescent girls hate the world. Well, brown adipose tissue (or
BAT, a better name than baby fat) is remarkable stuff. It's brown because
these adipose cells contain more mitochondria (the energy factories of our
cells) and mitochondria contain alot of iron.
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Sometimes
white adipose tissue helps you stay warm
too.
It is best if you have an even layer of fat over your
entire
body. Lynne Cox is such a person, and she can
do
long distance swims in freezing water – like
swimming
from a ship 2 miles to Antarctica.
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A UCP-1 protein (uncoupling protein) in the mitochondrial
membrane allows for energy (fat or glucose) to be burned without converting it to chemical
energy. More mitochondria in BAT means that even more heat can be produced. Babies
are smart!
And you can be smart too. You can teach yourself to make BAT
even if you’re not a baby. Recent research shows that cold acclimation can
induce BAT formation, and that the hormone melatonin can convert regular fat
(WhiteAT) to BAT. Other research
shows that your autonomic system can also turn WAT into BAT if stimulated to do
so.
So if you want to build the easily lost BAT instead of
hard to lose WAT – stay outside all winter. You will burn calories by
shivering and lose weight by burning BAT. After the snows, you’ll be so hot!
Contributed by Mark E. Lasbury, MS, MSEd, PhD
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