Stranded Hiker Patient
It is the middle of December and your patient has just been rescued via
helicopter from the top of Mt. Katahdin. It is 15 degrees F at 12pm, when your
patient was rescued. Winds were a sustained at 30mph. She was shivering and
complained of loss of feeling in her extremities. She told the first responders at the
scene that she had become disoriented at the summit, and was unable to locate the
way down. She had been curled up in the fetal position for 3 hours waiting for
rescue.
How Your Body Regulates Core Temperature
1. Vasodilation - increases surface blood flow, increases heat loss (when ambient
temperature is less that body temperature). Maximal vasodilation can increase
cutaneous blood flow to 3000 ml/minute (average flow is 300-500 ml/minute).
2. Vasoconstriction - decreases blood flow to periphery, decreases heat loss.
Maximal vasoconstriction can decrease cutaneous blood flow to 30 ml/minute.
3. Sweating - cools body through evaporative cooling
4. Shivering - generates heat through increase in chemical reactions required for
muscle activity. Visible shivering can maximally increase surface heat production by
500%. However, this is limited to a few hours because of depletion of muscle
glucose and the onset of fatigue.
5. Increasing/Decreasing Activity will cause corresponding increases in heat
production and decreases in heat production.
6. Behavioral Responses - putting on or taking off layers of clothing will result in
heat regulation
Arrector Pili Muscle
All hairs on the body grow from hair follicles located in the two uppermost layers of
skin. The arrector pili muscle is located in the dermis, the middle layer of skin, and
extends along the dermal root sheath. It is the muscle responsible for making hairs
"stand on end." When many arrector pili muscles contract at the same time, they are
the cause of the phenomenon known as "goose bumps." This unconscious reaction
The arrector pili muscle is composed of smooth muscles cells, and is therefore an
example of smooth muscle. Unlike the skeletal muscles that direct human
movement, for example, smooth muscle is not under conscious or voluntary control.
In furry mammals the contraction of the arrector pili muscle increases the animals'
protection from the cold. Raising the fur from the skin results in a layer of warm air
being trapped next to the skin. This layer of warm air acts as another layer of
insulation in addition to the fur. Raising the hairs also makes the fur thicker.
Thermoregulation
This is a bit different from mere insulation. In order to regulate temperature you
have to be able to both increase it and decrease it. Imagine walking outside on a hot
summer's day... it is hotter outside than your body temperature. How come you
don't overheat right away? How come you can stay outside for hours (if it is not
really, really hot) without passing out? Then you go inside. You enter an airconditioned building, which is set really low. It seems cold at first, but you "get used
to it." How come? What did your body do?
Your body handles these situations by having your skin respond to them. Your skin
can help you to lose or retain heat, depending on the situation. Kind of like having a
thermostat in your home that always keeps it at 72 ºF, whether it has to run the heat
or the air-conditioning to do it. Such a fancy thermostat in our homes would be
rather expensive. Our skin does it automatically, using only cellular energy.
Vasodilation and Vasoconstriction
The main way that our body handles temperature changes is by altering blood
vessel diameter in your skin. If you are too hot, then your blood is also too hot. You
can cool down the entire body by cooling down your blood. How? Dilate your
dermal blood vessels. Dilation increases their diameter, and since we have a
constant volume of blood that is running through our blood vessels under pressure,
if this blood has a lower pressure way to go, like through large vessels, it will. So
blood will flow into your dermal blood vessels. This causes it to run very near the
surface of your body, and allows for heat to escape from your blood quite easily into
the air. This makes the skin appear flush and red, and is usually accompanied by
sweating.
If you are too cold, you can warm up your body by constricting your dermal blood
vessels. This prevents too much blood from entering your skin, keeping it well
inside your body and away from any possible heat loss to the environment, and
close to your vital organs. Vasoconstriction is the narrowing of the blood vessels
resulting from contraction of the muscular wall of the vessels, in particular the large
arteries and small arterioles. This makes the skin turn paler because less blood
reaches the surface, reducing the radiation of heat.
Shivering- The human body has many amazing systems that help keep us running
smoothly through various conditions. Our body has homeostatic functions that
automatically monitor, adjust, and regulate our important systems without our even
knowing it, like breathing and heart rates. Shivering is just one of these homeostatic
functions our body employs to regulate our body temperature. We shiver in an
effort to keep ourselves warm.
Our brain both consciously and subconsciously detects cold simultaneously through
different sensory systems, which prompts the body to shiver — the sensory system
that prompts the shiver isn’t the same as our conscious detection of cold. Our body
attempts to maintain our core temperature of 98.6 degrees Fahrenheit (37 degrees
C), despite ambient temperature. In an attempt to avoid hypothermia where our
body temperature is lowered to dangerous levels, our muscles are prompted to
contract and expand quickly, resulting in a shiver. This in turn produces more heat
in the skeletal muscles to provide extra warmth to our organs. It does use a lot of
energy, and severe shivering is a last resort in an attempt to stay warm. Along with
shivering, your teeth may chatter due to tightening jaw muscles. It is usually the last
strategy the body uses to maintain its internal temperature to survive in a severe
cold environment.
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