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

Question

I have read something about why we die from too high or too low body temperature but have always found only general reasons. For example, that the liver fails. But why does the liver fail?

I would like to know the most fundamental reason why not possessing the appropriate body temperature can kill us. Ignoring the very extremes where it is I think obvious, such as temperatures below 0°C and above 100°C when water freezes and vaporizes.

I have supplied my reasonings below; if any reasoning here is wrong, please correct my thoughts.

As far as I understand, as the temperature changes, the speed of chemical reactions changes as well. As temperature goes up, the reactions occur faster and if the temperature decreases, the reactions slow down. So, if our body temperature changes, the speed of all reactions in our body change as well. Thus, with higher internal temperature we should just become 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 extremely high internal temperatures. So, is it that the speed of different reactions change with different rates, so the organism is not kept "in sync" and dies for that reason?

Or - as temperature changes, the volume of everything 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?

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.