I know people can get fevers up to +100f/37c. So why can’t our body just flip a switch and turn on a fever essentially. I have plenty of “stored” energy so I don’t see how that would be a problem.
In: Biology
To add context to the top answers – the reason why your body is more interested in conserving heat than it is in heating up is that most of your bodily processes will continue if you’re cold, and it takes a ton of energy (comparatively) to pump up the thermostat.
All of your body’s various nervous system functionalities are geared for survival. Survival is massively dependent on energy use. Your body manages its calories very carefully, and has a lot of mechanisms in place to store and hold onto calories. It’s why we get fat, and it’s why our ancestors were able to run down prey much larger than ourselves without tiring. Creation of heat takes a relative ton of calories – your body naturally creates some heat as a byproduct of your energy cycle, but creating more incurs an expensive calorie cost.
Actual regulation of bodily temperature is an important concept to survival – all of the proteins you have in your body are finely-tuned to work at 37°C/98.6°F. If your body goes appreciably above that, the proteins begin to denature (unravel) and lose functionality. When your body detects an immune response, it decides that the high calorie cost and potential protein/cellular damage is likely worth it to fight off the infection. This is why you feel like shit when you run a fever – your bodily processes aren’t working as efficiently. You’re sore (muscles are not as effectively repairing themselves / carting away metabolic byproducts as quickly), fatigued (less energy available because you’re running your internal furnace trying to burn out the infection), and with extreme fevers you’re probably delirious (actual damage to brain tissue caused by extreme fever denaturing proteins necessary for your brain to function).
So the question and answer with greater context, now; why doesn’t your body just turn up the thermostat when you’re feeling cold? Because between creating more heat and conserving the heat you already have, conservation is the one that will keep you alive longer per calorie spent. Vasoconstriction is the body’s method of triage when dealing with cold; check out your fingers next time they’re really cold, and you’ll notice that they are lighter in color. This is because the tissue in them has received a neural response to tightly clamp down on blood vessels, which lessens heat loss due to your blood circulating through that area. The concept is that less warm blood flowing out to your extremities, cooling, and then flowing back to your core to lower your core body temperature will keep you alive the longest at the lowest calorie count. Conserving the heat costs way less calories than making more of it. If instead you tried to keep the whole body warm all the time by producing more heat, you’d be dead way earlier due to radiating the heat away and having to keep producing more.
It’s 100% about survival. Your parasympathetic nervous system doesn’t know the difference between the A/C being up too high and you being stranded in the middle of a frozen tundra. It acts accordingly.
Edited to put more emphasis on the fact that it’s more expensive to produce more heat relative to conserving it. The overall goal is to maximize time survived per calorie.
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