A Little Bit More
We’re all familiar with dogs panting; this behavior is so common that it usually goes unnoticed. Humans pant too, when we’re especially active and our oxygen requirements are high. But this kind of “panting”, probably shared by all mammals during vigorous activity, is related to obtaining additional oxygen, and should not be confused with panting as a way of dissipating heat.
Panting in mammals to control temperature is a controlled increase in respiratory frequency with no increase in the amount of air taken into the lungs. During this kind of panting, air moves quickly through the respiratory passages (nose and mouth) where it can remove excess heat through evaporation.
Many mammals respond to heat stress by relying on evaporative cooling of sweat or panting. Evaporation of water requires energy. For a liquid (saliva or sweat) to become a gas requires energy in the form of heat. Thus heat is absorbed by the evaporating water in a dog’s nose and mouth, or on our skin and we’re cooled in the process. Panting does have two advantages over sweating. Panting results in little salt loss, and is effective in cool, still air – an environment in which sweating is not very efficient. Next time you see a dog or cat panting, you’ll know that it’s trying to cool its body down (unless it just finished strenuous physical activity).
Activities
Science – Cool Off
Objectives: Experience evaporative cooling
Materials: Water and make-shift fan
Although we’ve all experienced the evaporative process ourselves, it’s quite possible that many of us have never really thought about what was happening at the time. This is an extremely simple way to clearly demonstrate evaporative cooling and one that is definitely worth doing.
1. Select a student who can bare their arms
2. Designate one arm as the “dry” arm and one arm as the “wet” arm
3. Thoroughly moisten the “wet” arm
4. Now ask the student to hold both arms out from his/her body
5. Use a notebook or wide object to fan both dry and wet arms simultaneously
6. Ask the student which arm feels coolest – should be easy for student to decide
As the water evaporates from the skin, it absorbs heat from the subject’s arm so they feel cooler. A “dry” person who might be quite comfortable in a swimsuit at the beach becomes chilly when “wet” at that same beach under the same conditions.
Key Concepts
Adaptations and Diversity, Behavior and Regulation, Structures and Functions
Questions
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