What precisely happens when the body is deprived of liquids over a long period?
First, blood volume tends to shrink, surrendering part of its own constituent water to the kidneys, the sudoriferous glands, and the other excretory organs that remove toxins from the body. But blood volume cannot be reduced too much without causing loss of consciousness , as well as problems supplying the cells with the oxygen and nutrients they need.
It is therefore necessary for the body to adjust. As it is no longer receiving water from external sources, it must draw what it needs from the nearest internal source: the extracellular fluid. Unfortunately, this withdrawal means that the cells are no longer surrounded by a sufficient quantity of liquid, and this degrades their functioning so it is intermittent and incomplete.
The situation cannot help but continue to deteriorate, because the blood continues to give an uninterrupted supply of liquid to the excretory organs, forcing the interstitial compartment to give up its water. This reduction of interstitial liquid cannot go on for long without generating new disorders. The thickened interstitial fluid is no longer capable of ensuring that the exchanges between the blood and the cells take place as they should.
To remedy this, the body is again forced to find another solution, and begins to draw liquid from the intracellular fluid, withdrawing water the cells normally use when it's available but can do without if needed be. But the rest of their water is indispensable, and if the cells were forced to give it up, it would compromise their ability to function. If the body still does not obtain water from an external source, after taking all the other adaptive measures described, it draws water from this deep level of the body. The water content of the cells then shrinks inexorably, as the body has no other additional area from which it can withdraw water.
Overall dehydration of the body engenders two serious metabolic problems that are the main causes of all the various disorders caused by dehydration: enzymatic slowdown and autointoxication (poisoning by toxins produced within the body).
The role of enzymes is to perform the many biochemical transformations necessary for the body to function. To do this they need, among other things, an environment richly supplied with water.
When the volume of blood and cellular fluids shrinks, the substances normally held in suspension in them become more tightly packed. The body fluids become more highly concentrated, which gives the enzymes an environment poorly suited for their activity, a situation that continues to deteriorate as long as dehydration remains an issue.
At first, the enzymes continue to work, but at a slower pace. Later, this rhythm slows further, and the biochemical transformations become intermittent and incomplete.
Enzymatic slowdown eventually paralyzes all the body's activity, as the production of energy, hormones, reparative substances, and so on necessary for the body to perform properly gradually decreases.The influence of dehydration on physical abilities has been calculated to a very precise degree in sports medicine. The figures supplied by this research clearly show the speed with which dehydration has an effect on body function. A loss of liquid equivalent to 1 percent of total body weight is enough to diminish the body's working capacity by 10 percent. At a 2 percent loss, this capacity becomes 20 percent less efficient. The reduction in effectiveness continues at the same pace until around 10 percent, the stage at which the dehydrated individual loses consciousness, along with all motor and physical effectiveness.
For a person weighing 160 pounds, 1 percent of body weight is equal to 16 pounds, or 0.7 liter of water, a quantity that is easily lost through the sweat caused by one hour of physical exercise at an ambient temperature of 64 degrees Fahrenheit (18 degrees Celsius). At 82 degrees Fahrenheit, the hydric loss borders on 3 liters an hour, equaling more than 4 percent of total body weight and a 40 percent loss in physical ability.