big gurl hongry

Here in Alaska, the temperatures have dropped a good bit recently. We went from having highs in the 60’s to highs in the 20’s. Considering I’ve only ever lived in Texas, Louisiana, and Alabama and used to shiver at 60°, I’d say I’ve adapted very well. I have noticed an unexpected side effect however: increased grocery bill. I mean, like double. But what’s an endotherm to do?

I’m sure you’ve heard the terms “warm-blooded” and “cold-blooded.” Those are silly. Let’s use “endotherm” and “ectotherm.”  They describe an animal’s strategy to temperature regulation. You see, all animals have an optimal temperature at which their metabolic processes occur most efficiently. So life has developed ectothermy and endothermy as ways to maximize the bang for your buck. Or, energy for your food, as it were.

And herein lies a common misconception. Heat is not the end-goal of metabolism; you do not eat food for the purpose of heating your body. You- and all animals- eat food to power your systems, like the muscle fibers that contract to make your heart beat, or the network of brain cells that allow you to form thoughts. True, heat determines the efficiency of these functions, but does not directly power them.

As an endotherm, your body produces heat from the inside. Humans have evolved to produce- and dissipate- enough calories of heat to keep our bodies at a steady 98.6°. Each and every one of your living cells contributes a bit of by-product heat in the midst of its own chemical reactions to maintain this temperature.

Ectothermic animals absorb heat from their environment- not as a means of energy acquisition- but simply as a means of heat acquisition. They also dissipate heat to the environment- think of a snake hiding under leaves trying to escape the hot sun. Here, it is easier to see that heat ≠ energy when it comes to metabolism. It’s all about keeping the body at its optimum temperature- and for ectotherms, that temperature is usually significantly lower than that of endotherms- hence the warm/cold blooded silliness (but, the temperature of the blood of the animal doesn't determine nor describe how it temperature regulates- ectothermic and endothermic do. They win).

To me, the really interesting difference between endothermy and ectothermy is how they keep temperatures regulated: endothermy by physiology, ectothermy by behavior. Endotherms’ (mammals and birds) steady metabolic reactions take care of the temperature regulation for them. Ectotherms (reptiles, amphibians, fish, etc.) must actively scuttle between shade and sunny spots to either absorb heat or dissipate it, always trying for that sweet spot.

Hot breath from a dinosaur? Could it be?

You know that scene in Jurassic Park where the brother and sister are hiding in the kitchen and the velociraptor peers in through the kitchen window and fogs it up with its hot breath? Well, seeing as we know reptiles are ectotherms- what do you think of that? Have we caught good ole Spielberg in a blunder?

Of course we haven’t; he’s Steven Spielberg. Once an exothermic species reaches a certain size, heat from metabolism is actually unable to escape from the large body. The density and size of the body keeps internal heat from dissipating to the environment, in effect, making the animal endothermic. This is called gigantothermy- and all large dinosaurs are thought to have been gigantotherms. So indeed, a velociraptor would probably fog the window up with its breath before it ate your ass.

Now, I must go consume the family-sized portion of red beans and rice I made for supper. It’s frickin cold here, folks. Girl’s gotta supply her chemical pathways with carbohydrates and protein so they can release heat to keep her little body warm. Don’t judge.