Cold-Related Injuries #2

THE HUMAN ANIMAL

How do we stay warm? How do we produce heat? How do we regulate our core temperature?

Heat Regulatory Mechanism:
We “evolved” in the tropics and subtropics.
Therefore, we have a very sensitive and efficient heat regulatory mechanism.
We are naked, hairless, with sweat glands.
All warm-blooded animals use the evaporation of water to cool. 
Humans sweat; the evaporation of water off the skin cools the skin and blood.
Fur-covered mammals & birds pant, evaporating water out of the lungs thus cooling the pulmonary circulation.

Heat Production and Heat Loss

Heat Production: 
Basal metabolism, we burn glucose as a fuel to produce heat.
Metabolic activity set by thyroid, can be increased 5x’s.
Exercise - muscle activity.
Voluntary or involuntary = shivering, increases up to 10x’s.

Heat Conservation: 
Vasoconstriction in the skin.
Piloerection - hair stands on end.
Abolition of sweating.
           
Heat Loss: 
Conduction:  Transfer of heat from one solid object to another. 
0% - 40%  depending upon the type of solid material
Convection:  Transfer of heat from a solid object into the air or water. 
0% - 40% depending upon air penetration
Radiation:   Transfer of heat by infrared radiation. 
5% - 80% depending upon surrounding temperature
Evaporation:  Transfer of heat by the evaporation of water. 
0% - 90% depending upon vapor pressure & moisture

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