Hello, Readers! Our question for the day, asked by one of your own, is, “Why in the summer can your house be 65º and it feel great, but in the winter you are freezing?”
An excellent question, for which we must turn to biology for the answer.
First of all, the animal kingdom can be divided into two categories when it comes to temperature: Homeothermic/endothermic (warm-blooded) and poikilothermic/ectothermic (cold-blooded). The roots of these words give away their meanings: “Homeo” and “endo” for internal, “poikilo” for various, and “ecto” for external. Basically, does the animal rely on itself or the environment to maintain body temperature?
As we’ll see in just a bit, being an endotherm takes a lot of energy, so only birds and mammals make the effort. Most animals survive with an internal temperature between 32º to 113º F because at those extremes either the water in your cells freezes or your proteins, which do most of the heavy lifting, fall apart (respectively). On average, humans maintain an internal temperature of 98.6º F.
Now here’s where we begin to answer the question, and we’ll have to start with a sprinkle of physics. It is law -- the second law of thermodynamics -- that heat shalt move from a hot object to a cold one ‘til both are lukewarm. And the greater shalt be the temperature difference, the faster shalt be the movement.
So anytime it’s less than 98.6º F outside, heat is moving from our bodies to the environment. Most of the time we’re good with this, most of us actually preferring an environment at least 23.6º F (75º F) cooler than ourselves. But when it gets much cooler or hotter, our bodies compensate by either generating or losing more heat. And that brings us back to biology, with thermoreception and thermoregulation.
Thermoreception refers to how our bodies sense temperature changes, and as you might suspect they do it with thermoreceptors (or thermosensors). Our discussion of how these nerves work could go all the way down to DNA, but I’ll spare you the molecular details. The jist is that these nerves in your skin and organs send electrical impulses to your brain; and some like it hot, some like it cold.
For our question, we’ll focus on the thermoreceptors in your skin.
Thermoreceptors are like mothers; they send constant updates, so that even if the temperature isn’t changing, they will tell the brain about it. But when the temperature does change, they will send more signals more often until the temperature stops changing. It’s like the difference between “one Mississippi, two Mississippi, three Mississippi” and “one, two, three.”
Cold thermos do the most work, responding to temperatures at less than 93º F (normal skin temperature). At temperatures between 68º and 86º F, most cold thermos will return to their normal rate of signaling soon after the temperature stops changing.
So when the temperature goes from 75º to 70º F, you will at first feel colder, then the cold thermos will stop sending so many signals and you will feel comfortable at the new lower temperature.
But if the temperature drops below 68º F, the cold thermos will not stop sending rapid signals even if the temperature plateaus. Your body will adjust to this by making your blood vessels smaller, getting goosebumps, slowing your metabolism down, and shivering.
Now, let’s apply this knowledge to our question.
In the summer, the outside temperature in Indiana is normally between 75º and 95º F. Your body is working to lose heat, especially if you’re working or playing. You sweat and your blood vessels get larger.
Now you step into an air conditioned building, say between 65º and 72º F. Your body begins to lose heat much more quickly (remember the second thermodynamics law), which tells the thermos that the job is getting done, which your brain translates to you as relief. You stop sweating and your blood vessels return to their normal size.
But in the winter, when it’s anywhere from -20º to 40º F, your body is working to stay warm. You step into a building that’s heated to 65º F, which is warmer than outside, but is still not ideal (remember the cold thermos like it between 68º and 86º F). They tell your brain that the job is not done, which your brain translates to you as being frozen, so the shivering and such continues.
This constant tug-of-war between your internal temperature and the outside is known as thermoregulation.
All of this assumes all other variables are constant. Other factors like age, gender, health, and heredity can affect how your individual body feels and responds to changes in temperature.
Sources: “Thermoreception” and “Thermoregulation” at www.brittanica.com and “Thermoreception” and “Thermoregulation” at www.biology-online.org.