Maintaining the Right Amount of Water in Your Body

As much as three-quarters of the water in your body is in intracellular fluid, the liquid inside body cells. The rest is in extracellular fluid, which is all the other body liquids, such as

• Interstitial fluid (the fluid between cells)
• Blood plasma (the clear liquid in blood)
• Lymph (a clear, slightly yellow fluid collected from body tissues that flows through your lymph nodes and eventually into your blood vessels)
• Bodily secretions such as sweat, seminal fluid, and vaginal fluids
• Urine A healthy body has just the right amount of fluid inside and outside each cell, a situation medical folk call fluid balance. Maintaining your fluid balance is essential to life. If too little water is inside a cell, it shrivels and dies. If there’s too much water, the cell bursts.

Investigating the Many Ways Your Body Uses Water

Water is a solvent. It dissolves other substances and carries nutrients and
other material (such as blood cells) around the body, making it possible for
every organ to do its job. You need water to

• Digest food, dissolving nutrients so that they can pass through the intestinal cell walls into your bloodstream, and move food along throughyour intestinal tract
• Carry waste products out of your body
• Provide a medium in which biochemical reactions such as metabolism (digesting food, producing energy, and building tissue) occur
  
• Send electrical messages between cells so that your muscles can move, your eyes can see, your brain can think, and so on
  
• Regulate body temperature — cooling your body with moisture (perspiration) that evaporates on your skin
• Lubricate your moving parts