What is the fundamental reason for death from too high or low internal temperature?

Question

I have read something about why we die from over/underheat, but always found too general reasons. Such that the liver fails. But why does the liver fail? I would like to know the most fundamental reason why not having the right internal temperature can make us die. Ignoring the very extremes where it is I think obviuos, like temperatures below 0°C and above 100°C when the water freezes and vaporizes.

So, a little bit of what I thought could be the reasons. If anything here is wrong, please correct my thinking.

As far as I understood, as the temperature changes, the speed of chemical reactions changes as well. Temprerature goes up, the reactions happen faster and if the temperature decreases, the reactions slow down. So if our body temperature changes, the speed of everything in our body should change as well. So with higher internal temperature we should just be more active, speedy and so, and with low temperature we should become slower. But that does not fit into the fact that we die from too high internal temperature. So, is it that the speed of different reactions changes in different rates, so the organism is not kept "in sync" and dies for that reason?

Or - as temperature changes, the volume of all materials changes as well. I think that's called thermal expansion. But different materials have different rates of that process. So as our temperature changes, something inside us just literally breaks or deforms too much and we die?

So why do we (and other organisms) die from not having the right temperature? Am I on the right track or am I completely wrong? Thanks for any answer.

Jakub

Answer 1

As mentioned in the comments, half of your question is answered elsewhere. Generally you are right, different processes change at different rates. Blood viscosity changes. Some complex systems, such as the heart, may completely fail to function. The other half of your question has a simpler answer. As heat increases, yes in theory so should enzyme performance. However enzymes have a tendency to denature if they get too hot. When heat is excessive, heat shock proteins are released which are naturally stable in hot conditions and which attempt to stabilize other proteins. This is only possible up to a limited extent, and sufficient heat will cause proteins to become entirely non-functional.