Dehydration in Human Factors

Topics: Water, Dehydration, Blood Pages: 11 (1214 words) Published: June 1, 2014

Dehydration in Human Factors
Allan Gorge

Dehydration is an insidious disorder that plays a potentially deadly role in aviation and other aviation related specialties. We’ll take a look at the body’s composition of water, and the physiology of water loss and intake. We’ll also cover the different classifications of dehydration and there signs and symptoms. The dangers of dehydration in the role of aviation. As well as what you can do to detect and prevent dehydration.

The Role of Dehydration In Human Factors
Dehydration is defined as “Excessive loss of water from the body or from an organ or bodily part.”(The American Heritage Dictionary, Sec Ed) Water is the most abundant resource in the human body, and accounts for about two thirds of total body weight. This means a 150 lb man has roughly 10 gallons of water distributed throughout his body. (Merck Manual, Home Ed.) It’s seems hard to believe we’re carrying around that much water, let’s take a look at where we keep all that water. Take a look at the following picture to get an idea of the percent of body water through different stages in life.


Body Fluid Displacement
Water is divided into two categories inside the body; intracellular fluid (ICF) and extracellular fluid (ECF). Intracellular Fluid
This is the fluid located inside of body cells, accounting for roughly 70% of total body water. Extracellular Fluid
Accounting for the remaining 30% of body water, extracellular fluid is divided into two categories. Intravascular and interstitial fluid. Intravascular fluid; the fluid located in your circulatory system, or bloodstream. A typical adult male has on average 7 Liters of blood. Interstitial fluid is all remaining fluid not found in either the circulatory system or inside body cells, but located within the spaces between cells.

The water located in the bloodstream is certainly the most vital to body function, and the body is constantly trying to maintain homeostasis (balance). In order to do this the body has several compensatory mechanisms to deal with both excess fluid and fluid loss. Fluid Loss

The four primary routes of fluid loss are; urine through the kidneys, perspiration though the skin, water vapor through the lungs and gastrointestinal losses through vomiting, diarrhea and regular feces. There are other situations of fluid loss/and rehydration in trauma and burns, but that isn’t the focus of this paper and won’t be covered. The primary way to deal with fluid loss is through gastrointestinal absorption by simply drinking water or a sports drink such a Gatorade. However, when you don’t have an ice cold glass of water near by, the body must resort to its natural compensatory mechanisms. Generally speaking, when the body senses it’s low on water the sensation of thirst develops, the brain signals the pituitary gland (located at the base of the brain) to excrete ADH (antidiuretic hormone). This stimulates the kidneys to stop excreting urine and retain water. Water then begins to move from the 2 larger reservoirs of water, intracellular and extracellular fluid into the bloodstream through a process called osmosis. This along with vasoconstriction allows the body to maintain a blood pressure to adequately perfuse bodily tissues, the most important being the brain. Take a look at the following picture illustration the release of ADH from the pituitary gland.

Excess Fluid
In the case of excess body fluid, the opposite happens. The brain signals the pituitary gland to inhibit ADH production causing the kidneys to excrete urine. An increase in salivation may be present; the body also shifts water between the water of different body compartments.

It is important to note that dehydration not only involves water loss, but loss of electrolytes....

References: Berklow, R., & Md. Beers, M.H (1997) The Merck Manual of Medical Information
(Home Edition)
Bledsoe, B., Porter, R., & Shade, B., (1996) Paramedic Emergency Care, 3rd Edition
Why is Dehydration so dangerous?
Fairechild, D., Dehydration and Dry Cabin Air.
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