Hi, this is Kate from MinuteEarth. My temperature is just under 37 degrees Celsius -
98.6, for you Fahrenheit-ers - normal for a human. But here’s something weird about our temperature:
the highest body temp we know someone survived isn't that far above 'normal', but the
lowest is more than twice as far in the other direction. Why can we get so much colder
than we can hot, before our body calls it quits? It turns out that we’re already playing with fire,
as far as what’s happening inside our bodies. Proteins we rely on to perform critical biological
jobs work better when they’re toasty because heat loosens up their coiled structure, making them
flexible enough to interact with other molecules. Plus, warmer temps boost our immune system,
making it tough for germs to gain a foothold. But there is a limit to how hot any given
molecule in our body can get before it breaks. Over 40 degrees or so, certain proteins get
so loose that they start to uncoil completely. Not only can they no longer do their critical
jobs; uncoiled proteins start tangling up in tight clumps, which can gum up cells. This tangling
is what you’re seeing when you fry an egg, although the egg's hardy proteins can tolerate way
more heat than the delicate proteins in our cells. Other things start breaking above 40 degrees too;
membranes made of fatty molecules start to liquify and channels in and between our cells malfunction,
so stuff leaks where it isn’t supposed to. By the time our body reaches about 47 degrees, enough
critical components have broken down that we’re toast. Yet because of the benefits of warmth,
the human body - like the bodies of lots of other warm-blooded critters - has evolved to
operate pretty close to this breaking point, with only a little wiggle room for
the occasional fever or overexertion. There’s way more wiggle room in the
other direction. As molecules get colder, they become less prone to interacting, which
slows chemical reactions down. Your body can’t metabolize food as readily, electrical activity
in your brain decreases, and less blood gets pumped through your body. This slow-down isn’t
inherently deadly - it can actually be helpful, because the slower reactions happen, the less
energy and oxygen organs require. That’s why we chill organs before transplanting them and induce
hypothermia in people with brain injuries, and it’s part of how bears and other animals survive
huge wintertime drops in their body temperature. But there is a limit to how slow - and
therefore how low - you can go. Even cold, slowed-down organs require some blood flow
to supply life-sustaining resources and take away life-threatening toxins...without that,
we die. But as long as the temperature of a person - or a snoozing bear - stays just
high enough to keep our organs working, we can generally reverse the
problems caused by cold...just warm up again (slowly!) and things
will go more or less back to normal. This bear-y awesome video was sponsored
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