Sweating

[Riogho]

Okay, I understand (basically) how sweating works. Your sweat glands, when you're hot, produce sweat and the sweat evaporates taking heat energy away, therefore cooling you off.

 

A question I had was if you were submerged in water but still above the temperature that causes you to sweat, would you sweat underwater?

[Mr Skeptic]

I think you would still sweat, but it wouldn't help you. And you'd cook.

[iNow]

Yes, being underwater does not alter your basic physiology, so you'd still sweat when you're too hot (ever taken a hot bath? it makes you sweat). What changes is the effectiveness of that response in terms of dropping your body temperature.

[big314mp]

I think it's why you aren't supposed to spend very long in hot tubs - impaired cooling + improved heat transfer into the body.

[swansont]

Once the sweat doesn't evaporate it doesn't do you much good, but your body doesn't really "know" this, so you sweat and sweat. It's the body's reaction to being too hot.

 

My very first blog post was about this http://blogs.scienceforums.net/swansont/archives/1

[pioneer]

Life fixes water making it harder to evaporate. The soil around a plant will evaporate first, then the plant loses its water. Evaporating water from salt water gets harder and harder as the salt concentration increases, because the water binds better to the salt the more salt you have. Life sort of does this, with cells doing their chemical attraction thing to water in a slightly different way.

 

If we heat a brine solution, but below boiling, the vapor pressure will increase with temperature because the heat allows more water to gain the energy needed to evaporate. This will still be less than pure water, but it will still generate a vapor pressure. The body is the same way, with heat, helping to break the bonding forces in the cells that bind the water. The sweating, by evaporating, adds a cooling affect, which lowers the evaporation rate. Once we cool the cells can bind water better and the output lowers.

 

The body has evolved to do this in an efficient way by setting up other barriers for water retention. But if you think of it, the body is 80% water with all the water touching. The sweating is for a net affect, just like the pot of brine boils as a unit. Heating and cooling occurs on the surfaces but conducts.

 

The sweat is not pure water but is salt water. This is smart, because if it was pure water sweat, the salts would build up in the body and would retain the water stronger. We would stop sweating sooner causing the body to overheat much sooner. The salt in the sweat also lowers the vapor pressure of the water, so the sweat will last a little longer. A pure water sweat would give a stronger but shorter cooling burst. We get a slower but longer cooling affect by adding salt. This second is much more versatile.

 

At the same time, the chemical potential between the body and the sweat is lower with salty sweat, compared to pure water sweat. The result is the cooling affect takes less energy, allowing the heat to almost be enough. To make pure water sweat, the body would have to expend energy to run an osmosis. The salt sweat can almost skip this higher energy step because it requires something closer to just the extra body heat to run the sweat process (more or less). The more heat the more we sweat.