Water is the most important nutrient. You can lose most of your body fat and even protein, but losing more than 12% of your body water will be fatal.
Water has 3 very important properties that help it be so useful:
Water has many functions in the body:
Effects of water restriction include:
+H
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O = Something like that
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+H
Because opposite charges attract, this makes a good medium in which to dissolve things that dissociate and have a charge, as most things do. An example is sodium chloride (salt)
NaCl ---> Na+ + Cl-
Therefore water is often considered "the universal solvent", which it isn't of course, but it does dissolve many things.
Water has a high specific heat, which means that it takes a lot of energy to change the temperature of water very much. This helps maintain a constant body temperature by resisting temperature change with energy input, as for example, when we exercise.
Another example of the effect of high specific heat is demonstrated by the story I tell in class about peaches from West Lafayette versus peaches from Michigan. The story is: ours usually fail while Michigan, which is farther north and usually colder, produces peaches. Why? Lake effects. The large body of water acts as a 'heat sink' and affects the climate of the area around it.
Water has a high latent heat of vaporization. This means that it takes a lot of energy to transform water from liquid to vaporous state. Or the other way around, a lot of heat transfer takes place when water changes to vapor from liquid.
So, when an animal sweats, it has a large cooling effect, removing heat from the animal's body. Likewise, when you see a dog in the hot summer, lying in the shade of a tree and panting shallowly, he is cooling himself by transferring water out of the body in vapor form in exhaled breath. The shallow breathing keeps it from hyperventilating.