How is do warm blooded mammals generate the excess heat to maintain body temperature?
I’m asking about specific fuelstocks and chemical reactions.
If normal metabolism produces sufficient heat, and most of thermoregulation is about preventing overheating (e.g sweating), what’s different about “cold blooded” organisms’ metabolisms to make the heat produced by normal metabolic activity insufficient? They simply burn slower, so to speak?
What’s the hypothesis on why humans don’t have “brown fat” stores?
Bonus: What’s the species of snake that uses thermogenerative shivering?
Fairly complex question, but in general they mammals do just make use of normal metabolic heat. When we are too cold we deliberately exploit large muscles groups to generate heat without generating any movement, that’s what’s called shivering. As you’ve alluded to yourself many mammals, including humans, can utilise a special type of fat called brown adipose tissue that generates heat as it’s burned. So it’s not correct to say that humans don’t have any BAT stores, it’s just that they are exhausted within 6 months of birth and we never regenerate them. AFAIK humans aren’t particularly special in this regard and most adult mammals lack BAT.
Ignoring BAT there’s no special fuelstocks used, just the normal stuff used for maintaining membrane potentials and resetting the muscle fibres, mainly ATP via glucose.
Normal metabolism doesn’t produce sufficient heat to keep mammals running. Even in the tropics in the middle of summer sedentary mammals will usually be forced to resort to shivering to maintain their temperature for a few hours a night, and in winter they’ll be doing that most of the day. Outside the tropics.subtropics sedentary mammals won’t be able to maintain their body temperature without shivering for much of they year. Remember that most shivering doesn’t take the form of violent fits, they tend to be smaller reactions that might not be visible.
Cold blooded animals don’t necessarily burn slower. Indeed many of them are quite a lot warmer than mammals when they are active. The difference is that they need to be active to stay warmer than the environment. As soon as they stop to rest their body temperature falls because there is nothing being done to maintain it. Many cold blooded animals actually have special blood shunts designed to keep the heat from active muscles within those muscles so they don’t cool down while the rest of the body can remain much colder,
What’s the species of snake that uses thermogenerative shivering? Most of them AFAIK. It’s quite common amongst all the pythons AFAIK to shiver to generate heat by shivering, especially after ingesting a large meal.
How small are we talking about? Because, being a fairly smart mammal, I’d like to think I could tell when I’m shivering… yet you’ve just told me I’m shivering most of the year for thermal homeostasis.