Yes. Your body will replace the fuel stores, but to do that water needs to go in with it.

Water increases in proportion to muscle creatine phosphate and glycogen content. Both fuels are used up during exercise, and the water leaves the cell. As your body replaces the fuels you depleted, water goes in with it to maintain the osmotic balance. Plus there are probably hundreds of other cellular processes activated that require water in some capacity.

Repeated short term exposure to heat (without heat stroke) causes many of the same adaptations as exercise training including plasma volume expansion, improved cardiac output, decrease sweat sodium concentration, and increased thermoregulation capabilities. This makes a person less likely to suffer heatstroke.

I would imagine there could be permanent damage related to severe heat stroke, but I would be surprised if it made people more likely to suffer subsequent heat stroke (as one commenter liked to an article about). Anecdotally I know many people who’ve been hospitalized with heat stroke but have no issues in the heat subsequent to the initial incident

Your body saves carbs as much as possible. If it can use fat, it will. Think of carbs as only being used if your body has to - to go fast (or in the brain)

Muscle cells can take up glucose from the bloodstream through their own transporters without the need for insulin.

When you’re regularly active, your muscles pull the glucose out of the blood, effectively regulating your blood glucose without insulin needing to be involved. This allows all the cells in the body to readjust the number of insulin-receptors/glucose transporters needed, thereby making you more sensitive to insulin over time, and the pancreas won’t have to release as much insulin for any given amount of glucose in the blood.

Obviously it’s way more complex than this, but even with oxygen, if the glycolysis rate is high, not all pyruvate gets into the mitochondria. U/metacelcus explains it better, but a simpler explanation I use is to think of it like a sink faucet that’s turned up so high that the drain can’t drain it fast, and some water overflows the basin. In this case, glucose to pyruvate is the faucet, the drain is the mitochondria and the overflow is the formation of lactate. It’s not a perfect analogy, but does reasonably well to get the concept across in undergrad exercise physiology classes.

There are a number of ways to induce various maladies to create animal models of diseases. Some ways are genetic, some environmental, some through selective breeding, some through nutrition, and many other ways. Most animal research however doesn’t use primates (aside from humans). Mice are often the go to for mammalian research. Their genome is well understood and relatively easily modifiable. For instance, we can modify a gene that makes them less sensitive to insulin and thereby they effectively have type II diabetes. Sometimes some animals naturally have genetic abnormalities that make them good animal models for human diseases. Golden retrievers actually experience something very similar to Duchenne Muscular Dystrophy, and through selective breeding, a colony of dystrophic dogs was managed to study the impacts of treatments that might be viable for humans. Sometimes we also find animals in the wild too. There’s a species of monkeys, I think in Central or South America, that are spontaneously hypertensive and they’ve been used to better understand high blood pressure in humans. For most common human diseases though, you can almost guarantee an animal model has been found or developed. Just type in the disease followed by “animal model” in Google and you’ll find fascinating stuff.

The damaged cells release chemical signals that signal to nearby cells which starts the healing process. Many tissues have stem cells sitting there just waiting for that signal and they jump into action when they get the signal.