How does the human body manage extreme cold?
Mid to late January is, on average, the coldest time in Minnesota — and it appears winter is right on schedule this week.
Turns out, the human body is designed to play defense in this weather.
It's a saying Minnesotans and Wisconsinites know well: "There's no such thing as bad weather, just bad clothing."
The problem is that even proper clothing might not be enough to withstand the bitter chill headed for the bold north, as the forecast shows consecutive days in which the high temperature stays below zero degrees from Thursday night to Sunday afternoon.
How does the human body manage extreme cold?
"Our body sends signals to our brain to say we need to do something about this and so, there's a variety of things that happen," Dr. Megan Rishcall, an emergency physician with Hennepin Healthcare, said.
First, our blood vessels constrict in our arms and legs.
"So we're shunting that nice warm blood to our core, to our heart and our brains. We need our heart to stay warm because once our heart gets cold, it stops beating," she said.
We also start to shiver, which raises our body temperature. Then, certain behaviors are triggered to create warmth.
"You'll notice when you're out in the cold, you'll start to rub your hands together, start to move around," Rischall said, adding that you'll instinctually seek indoor environments or try to cover up.
Losing feeling in our extremities and shivering are clear signs that we are cold. But what symptoms would signal something worse, like hypothermia?
"We start to get a little confused and sometimes people will get a little bit just agitated or just seem kind of out of it and that can be an early sign of hypothermia setting in," Rischall said.
If you can't remove yourself from the extremely cold environment, the hypothermia symptoms worsen.
"The shivering mechanism stops and we're no longer able to heat ourselves. That's when things get really dangerous. That's when the heart rate starts to slow and that's when we get very confused and can even collapse into a coma," she said.
Our eyes are wet and uniquely exposed. So, what keeps our eyes from freezing in extreme cold?
First, their location in our head. As Rischall said, blood flow is prioritized to the head area, keeping the eyes warm.
"But also, when we get cold, we're triggered to blink and we do have the tear production which helps protect our cornea, which is that outer layer of our eye," she said.
On top of that, our tears are salty, lowering the temperature they freeze. So the eyes' location, protection from blinking eyelids and constant tear production work in unison to keep them from freezing.