Tuesday, December 9, 2014

Winter Gives Me The Shakes

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.
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.

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.

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.
The ANS is also connected to your emotional state. Things like the fight or flight response aren’t under your voluntary control. So when you get the heebie jeebies, the ANS initiates responses for you to deal with it; your arrector pili muscles just come along for the ride. As a result, fear or eerie feelings may bring on goosebumps. Step on your cat’s tail and you’ll get a great demonstration of the arrector pili action independent of thermoregulation.

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.

Hairy Rob Lowe couldn’t freeze to death he tried.
He looks like he’s wearing a sweater even
when in the bathtub.

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.

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.
Vasoconstriction comes at a price. We discussed last week how constricting the surface vessels in your appendages (toes, fingers, nose, ear lobes) makes them more vulnerable to frostbite because there is less warm blood flowing through them. Evolution says its better to lose a toe to the cold than to lose all your heat to the environment and die from hypothermia.

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.

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.
Mitochondria use carbohydrates or fat to make chemical energy, and a bit is lost as heat. But what if you disconnected the making of chemical energy from the burning of carbohydrates and just let all of the energy be lost as heat? It’s called non-shivering thermogenesis; a pretty cool trick - pun intended.

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

Torkamani, N., Jones, L., Rufaut, N., & Sinclair, R. (2014). Beyond goosebumps: Does the arrector pili muscle have a role in hair loss? International Journal of Trichology, 6 (3) DOI: 10.4103/0974-7753.139077

Jiménez-Aranda, A., Fernández-Vázquez, G., Campos, D., Tassi, M., Velasco-Perez, L., Tan, D., Reiter, R., & Agil, A. (2013). Melatonin induces browning of inguinal white adipose tissue in Zucker diabetic fatty rats Journal of Pineal Research DOI: 10.1111/jpi.12089

Lim, S., Honek, J., Xue, Y., Seki, T., Cao, Z., Andersson, P., Yang, X., Hosaka, K., & Cao, Y. (2012). Cold-induced activation of brown adipose tissue and adipose angiogenesis in mice Nature Protocols, 7 (3), 606-615 DOI: 10.1038/nprot.2012.013

Bi, S., & Li, L. (2013). Browning of white adipose tissue: role of hypothalamic signaling Annals of the New York Academy of Sciences, 1302 (1), 30-34 DOI: 10.1111/nyas.12258

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