As a native Chicagoan, I know the importance of covering your head in the winter (you lose 90% of your body heat blah blah blah…). My question is why is the head the primary area of heat loss.
Is there some perfect combination of capillaries close to the skin, little body fat (for most Dopers at least), and other biological activity going on that makes the head perfect for losing heat? Or is it simply because it’s at the top of your body, and heat rises?
My anatomical/biological Ignorance needs fightin’!
Story: The wife and I were lying in bed, when she announces she’s cold. “I’ll help,” I say, as I skooch over to aid the lady in distress. Then the cat jumps onto the bed and wedges itself into its usual spot between my wide’s head and the headboard. So I say, “And now the cat is your hat to keep in your body heat”.
And then one quiet moment later I say, “But I don’t know if that works when you’re lying down”. My wife laughs a ittle bit, realizes I’m serious, looks slightly concerned for my sanity.
“You know, because maybe you only lose heat through your head, because it’s at the top.” She ponders that for a moment. “Hmmm. Maybe.”
Heat itself does not rise; hot fluids tend to rise above cold ones, where they have the opportunity to flow more or less freely.
A significant portion of your circulatory system is devoted to providing copious blood flow to your brain; your head is an extremity and is not usually covered; this all adds up to heat loss. (your other extremities shut down circulation if they lose too much heat, but your head can’t afford to do that).
I believe recent studies/analyses have shown that heat loss from the head is not as much as we were taught. Nevertheless, while the body is programmed to shut down circulation to fingers and toes, possibly even sacrificing them (frostbite, etc.) to maintain critical heat, it obviously won’t do that to the brain. I’m not sure how the scalp figures in, but it has a large surface area with blood vessels right by the skin. And that same surface area is available for heat from the brain, which I suspect has precious little – if any – insulation, to escape.
In contrast, other key organs are nestled in the core with a much more favorable surface area-to-volume ratio, and a significant amount of insulating fat and muscle.
It’s a great sentence, but no, and I don’t see where the responses here support it. Lying down or standing up, there’s still nothing between the brain and the cold but the skull, the scalp, and hair (which is of minimal help), although the downward side of the head may be insulated if you’re not lying on a heat sink (e.g. the ground). The face, forehead aside, has muscle and fat and eyeballs and such for insulation, which help, but usually is at least partly exposed for purposes of breathing and seeing, which doesn’t help. But those things aren’t changed when lying down.
However, the great thing about a cat is that it’s not just insulation, but an active heat source (I assume you’re not using a dead cat). The trick is making sure the cat doesn’t want to knead your scalp.
Because in the original study that determined people lost 90% of their body heat through their head, they were standing in a polar region wearing incredibly insulating clothing everywhere else.
But the coolest (so to speak) thing would be to wear Schroedinger’s cat. That way it could be either dead or alive, depending on the way you or others observed it. The best of both worlds!
While other people have already noted that the amount of heat loss through the head is exaggerated or misrepresented, it also bears consideration that some particular appendages, namely the ears, are designed (well, evolved) to radiate extra heat, which is why our ears stick out so far and are so convoluted. If you feel your ears on a warm summer day (when the temperature is above body temperature, or you’ve been exercising) you’ll find that the ears are hot!
Heat loss from the brain case itself is fairly minimal. Bone is a pretty good thermal insulator and the brain is the only organ that is almost completely surrounded by bone. But there are numerous capillaries running on the outside of the skull under and in the skin, in which there is virtually no fat to insulate. (Human fat is a rather poor insulator in any case, giving lie to the notion that obesity is some kind of justification for Aquatic Ape Hypothesis.) Hair does provide some insulation, particularly as a wind break, but humans were not evolved to live in Arctic or subArctic regions, and so heat loss in winter says little about why the body evolved to radiate heat the way it does.
In any case, the brain and nearby tissues receive a prince’s share of warm, fresh blood given that it isn’t a muscle and doesn’t have any principle role in digestion. It’s not surprising that a significant amount of heat. So, when the cold Chicago wind blows, style up with a hat. I prefer a fedora, but then, I live in SunSoCal where I barely have an excuse to wear a hat at all.
