Getting old sucks! It’s even worse if you’re a dog, since your parts reach their expiration dates that much more quickly.
That’s the issue that we ran into with Keely recently. After six years of carefree ball chasing, she’s developed arthritis in her cranial cruciate ligament (the canine equivalent of our ACL). The effect of her condition is that she’s no longer allowed to do anything that would cause her to turn sharply, especially chasing a ball.
As I was digesting this bittersweet news, the vet added, “But, she’s in great shape to keep running. Just pay careful attention to how she’s panting. It’s starting to get hotter out there.”
We all know about the dangers of dehydration and hyperthermia, but how often have you thought about the mechanisms involved in keeping yourself cool?
If you’re anything like me, I’m sure the answer is never. Or, at least, only during the dog days of summer, pun intended.
However, something about what the vet said piqued my curiosity. I needed to find out more.
Evaporative cooling is all wet
When it comes to keeping cool, there are really three major mechanisms at play: evaporation, insulation, and metabolic regulation.
Think of insulation like wearing white linen, or sitting under an umbrella on a sunny day. Animals that have adapted to living in desert climates, like camels, often develop thick coats of fur that serve to – perhaps counterintuitively – prevent the transfer of heat from the environment to the animal. This occurs partially due to evaporative forces under the coat, and partially through reflection of direct sunlight.
Metabolic regulation is one I think most of us are familiar with. It’s the urge to just lay around doing nothing on hot days and, may I say, guilty!
However, evaporative cooling is the method we’re most concerned with.
During evaporation, water absorbs a tremendous amount of energy in order to break the powerful hydrogen bonds. In layman’s terms, it takes a lot of heat to make steam. Heat that gets used in the evaporative process is heat that isn’t being transfered to the body.
To sweat, or to pant
As human beings, we get off fairly easily when it comes to evaporative cooling. Sweating is a very efficient form of cooling and we’re well designed to take advantage of it. Eccrine glands excrete water to the surface of the body, and air moving over it provides the energy necessary for evaporation. No work required!
Talk about lucky. In fact, only primates and certain species of ungulates sweat.
Unlike sweating, panting requires the active participation of the animal involved to produce the air current. Of course, some animals have adapted to provide all the surface area and exposure necessary.
However, for those animals that aren’t part aardvark (which is all of them except aardvarks and, apparently, my dog), the mechanical energy required to pant can actually raise their core body temperature.
At the same time, since the evaporation is occurring in the mouth, the act of panting acts locally to lower brain temperature. In that sense, it can be more effective for severe cases of overheating. It’s even been observed in the African gazelle to account for a difference of as much as 3° Celsius between core and brain temperature. A similar difference was recorded in the chuckwalla.
So, what do you think? Is our sweating an evolutionary advantage or a handicap? Should I let my tongue hang loose and pant my way through my next marathon? Leave me some love in the comments.