Re: How does the body heat up and cool down?

Good question Andrew,

Since I am not sure what grade you are in, I will assume that you are in 
elementary school.  How the body heats up is not exactly known.  What we do 
know is that it takes energy to heat the body up, just like a house.  
Instead of gas or electricity, it is food that provides the energy to heat 
our body.  You can think of the body "burning" the food inside of us, like 
burning wood in a fireplace.  Some of the energy is in the form of heat to 
warm our body, while some of the energy is used to help our muscles move.  
If you eat a lot more food that you need, the extra energy from the food is 
stored away as fat on your body.  Sometime it is so cold, that our skin 
gets goose bumps and our body shivers.  When that happens, we are 
exercising tiny muscles under our skin and the muscles of our arms and legs 
to burn up more of the energy from food or from fat to make more body heat.

To cool down the body when it is too hot, like after a basketball game in 
August, there are two ways.  The first way that you probably know of is 
that we sweat.  Our sweat cools us down because our body's heat is absorbed 
by the sweat and leaves us as it evaporates, or if we wipe it away.  This 
is a very important way of cooling down.  When sweat or water evaporates 
from our skin, it takes a lot of heat with it.  That is why it is important 
to drink liquids when it is hot outside.  The second way is that our blood 
vessels under our skin begin to carry more blood to the surface of our body 
to release it.  This causes our face to look more red sometimes.  Have you 
ever noticed that some of the other kids get red in the face after playing 
on a hot day?  Now you know why!


Andrew, if you have had some biology, here's the more complicated answer:

Our body is heated through the same process that is used to generate energy 
in the form of ATP (metabolism). You can imagine that instead of making 
more ATP from nutrients, the body becomes less "efficient" and "wastes" 
some of the energy in the form of heat.  Brown fat tissue is a major factor 
in keeping some cold-tolerant mammals warm by uncoupling metabolism from 
generating ATP and directing it towards more heat generation.  The exact 
mechanisms governing the way humans generate heat are not exactly known.  
But we do know that thyroid hormone is responsible for how much heat our 
body generates (in a non-exercising or shivering kind of way).  In patients 
who have too much thyroid hormone (like Grave's disease), these patients 
will complain of always feeling hot.  In the opposite direction, patients 
with too little thyroid hormone will always complain of feeling cold.  
Aside from shivering, our body will also try to conserve the heat it has 
when it is cold out by reducing the flow of blood to capillaries near the 
skin's surface.  

To cool down, it is essentially as I have described earlier. 

Hope this helps!

....mark fung, md/phd