Think of what you need to survive, really just survive. Food? Water? Air? Facebook? Naturally, I'm going to concentrate on water here. Water is of major importance to all living things; in some organisms, up to 90% of their body weight comes from water. Up to 60% of the human adult body is water.
According to H.H. Mitchell, Journal of Biological Chemistry 158, the brain and heart are composed of 73% water, and the lungs are about 83% water. The skin contains 64% water, muscles and kidneys are 79%, and even the bones are watery: 31%.
Each day humans must consume a certain amount of water to survive. Of course, this varies according to age and gender, and also by where someone lives. Generally, an adult male needs about 3 liters per day while an adult female needs about 2.2 liters per day. Some of this water is gotten in food.
Water serves a number of essential functions to keep us all going:
According to Dr. Jeffrey Utz, Neuroscience, pediatric. . . . . . .read more at http://water.usgs.gov/edu/propertyyou.html
- A vital nutrient to the life of every cell, acts first as a building material.
- It regulates our internal body temperature by sweating and respiration
- The carbohydrates and proteins that our bodies use as food are metabolized and transported by water in the bloodstream;
- It assists in flushing waste mainly through urination
- acts as a shock absorber for brain, spinal cord, and fetus
- forms saliva
- lubricates joints
- Intracellular fluid (2/3 of body water) is fluid contained within cells. In a body containing 40 litres of fluid (ie. about 72 kg total weight), about 25 litres is intracellular, which amounts to 62.5% (5/8), close enough to the 2/3 rule of thumb. Jackson's texts states 70% of body fluid is intracellular.
- Extracellular fluid (1/3 of body water) is fluid contained in areas outside of cells. For a 40 litre body, about 15 litres is extracellular, which amounts to 37.5% Again, this is close to the 1/3 rule of thumb cited here.
- Plasma (1/5 of extracellular fluid). Of the 15 litres of extracellular fluid, plasma volume averages 3 litres. This amounts to 20%, the same as per Netter's Atlas.
- Interstitial fluid (4/5 of extracellular fluid)
- Transcellular fluid (a.k.a. "third space," normally ignored in calculations) contained inside organs, such as the gastrointestinal, cerebrospinal, peritoneal, and ocular fluids.
Dilution and equilibration
- total body water: tritiated water or heavy water.
- extracellular fluid: inulin
- blood plasma: Evans blue