|MadSci Network: General Biology|
Water makes up about 2/3 or 67% of the human body. Over half of the water in our bodies is intracellular ( found inside the cells ), and less than half is extracelluar ( outside the cells in the spaces between the cells and in the blood ). Water has several functions in our bodies. It acts as a solvent for chemicals. That is, all the chemicals we need for reactions to happen in our bodies to keep us going have to be dissolved in water in order to work and to cross cell membranes (cell wall). Water also helps to keep each of our cells in the size and shape they are supposed to be. The brain can detect when our bodies are too low in water (usually when the salts and sugars in our blood and body fluids are too concentrated); that's when we get thirsty. The best thing to drink when we get thirsty is plain water. Reference: How the Body Works, Steve Parker, Reader's Digest 1994
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