By Ed Brown, EMSCI #002T/PCI #178T
Orange County Fire/Rescue (FL)
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All of us are aware of the importance
of the intake of water. But perhaps we may not be aware of the demands our
bodies place on this special ingredient.
The American Heritage Dictionary describes water as a clear, colorless, nearly
odorless and tasteless liquid, H2O, essential for most plant and animal life
and the most widely used of all solvents.
Water? Clear, colorless, odorless, and tasteless. Why even consider it? And
a chemical formula of two parts hydrogen and one part oxygen, does that even
sound good? No way! Yet water is the substance our bodies most require. Here
is a look at the medical side of the importance of water, according to the
2nd Edition of Paramedic Emergency Care by Bledsoe, Porter, and Shade.
Water is the most abundant substance in the human body. In fact, water comprises
approximately 60% of total body weight. The total amount of water in the
body at any given time is referred to as the total body water (TBW). The
TBW of a person weighing 70 kilograms (154 pounds) is approximately 42 liters
(11 gallons).
Water is usually distributed into various compartments of the body. These
compartments are separated by cell membranes. Approximately 75% of all body
water is found in the intracellular compartment, which contains all fluid
found inside body cells. The extracellular compartment contains the remaining
25% of all body water, or extracellular fluid.
There are two divisions within the extracellular compartment. The first includes
the intravascular fluid - the fluid found outside of cells and within the
circulatory system. It is essentially the same as the blood plasma. The remaining
compartment includes the interstitial fluid - all the fluid found outside
of the cell membranes, yet not within the circulatory system.
Water is the universal solvent and is necessary for many of the biochemical
reactions that occur. The water coming into the body is referred to as intake.
The water excreted from the body is referred to as output. To maintain balance,
the intake must equal the output.
Several mechanisms work to maintain a relative balance between input and
output, i.e., when the fluid volume drops, the pituitary gland at the base
of the brain secretes the hormone ADH (anti-diuretic hormone.) ADH causes
the kidney tubules to reabsorb more water back into the blood and to excrete
less urine. This process helps restore the fluid volume to normal values.
Thirst also regulates fluid intake. The sensation of thirst normally occurs
when body fluids decrease, stimulating the person to take in more fluids
orally. On the other hand, when too many fluids enter the body, the kidneys
are activated and more urine is excreted, thus extra fluids are eliminated.
The body also maintains fluid balance by shifting water from one body part
to another.
An individual performing work in a hot environment will lose one to two liters
of water per hour. Each liter lost contains 20-50 millequivalents of sodium.
The loss of water and sodium, combined with general vasodilation, leads to
a decreased circulating blood volume, venous pooling, and reduced cardiac
output.
Remember: even though all this medical knowledge about the importance of
water may not mean that much to you, summer weather is upon us and dehydration
might be just around the corner. Dehydration can lead to heat cramps, heat
exhaustion, and heat stroke. So monitor yourself, your fellow cyclists, your
workload, and the temperature. And never forget to practice what we preach:
Drink BEFORE you are thirsty.
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