Dehydration

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Related to Hypohydration: hyperhydration

dehydration

[‚dē·hī′drā·shən]
(chemistry)
Removal of water from any substance.
(organic chemistry)
An elimination reaction in which a molecule loses both a hydroxyl group (OH) and a hydrogen atom (H) that was bonded to an adjacent carbon.

Dehydration

 

splitting off of water from organic or inorganic compounds. Dehydration can be achieved thermally (mostly in the presence of catalysts) or chemically by the action of dehydrating agents (water-binding substances). The formation of ethylene from ethyl alcohol is an example of dehydration performed by passing ethyl alcohol through a tube containing aluminum oxide (catalyst) at 300°–400°C or by heating it with concentrated sulfuric acid (dehydrating agent) to 170°C:

CH3 —CH2OH → CH2 ═CH2 + H2O

The formation of ethylene is an example of intramolecular dehydration. However, heating the excess of ethyl alcohol with sulfuric acid to 140°C leads mainly to intermolecular dehydration with the resulting formation of diethyl ether:

CH3CH2 —O—H + H—O—CH2CH3 → CH3CH2 —O—CH2CH3 + H2O

Intramolecular dehydration of acetic acid CH3COOH yields ketene CH2=C=O, whereas the intermolecular dehydration of acetic acid yields acetic anhydride (CH3CO)2O. Dehydration of the amides CH3CONH2 yields nitriles CH3C≡N. Formation of nitrogen pentoxide from nitric acid in the presence of phosphorus pentoxide is an example of the dehydration of an inorganic substance:

Dehydration also includes the processes leading to the removal of water of crystallization from crystal hydrates and the removal of water bound by adsorption forces. Dehydration is the opposite of hydration.

B. L. DIATKIN


Dehydration

 

loss of water by an organism to a point below the physiological norm. Animals die when they lose 20–25 percent of their body water, and disorders arise when the water loss reaches 10 percent. Dehydration may develop as a result of excessive water loss (repeated vomiting, diarrhea, excessive perspiration, extensive burns) or restriction of water intake.

Excessive water loss leads to hypo-osmolar dehydration, a condition in which the body loses a significant quantity of electrolytes along with the excreted fluids, the osmotic pressure in the cells is higher than in the interstices of tissues, and fluid enters the cells. When the water intake is restricted, the loss of fluid substantially exceeds the loss of electrolytes. This leads to hyperosmolar dehydration, a condition in which the osmotic pressure in the interstices of tissues increases and water passes from the cells to the extracellular space, as a result of which the cells become dehydrated and die.

Dehydration is accompanied by agonizing thirst, which is more difficult to endure than the hunger caused by deprivation of food. The secretion of all digestive glands is reduced, the blood thickens, and the blood viscosity increases. The changes in the blood lead to serious disorders of blood circulation and to disruption of renal function. Acute dehydration may lead to mental disorders, collapse, and sometimes death. Dehydration develops considerably more rapidly in children than in adults, since in children, especially infants, the amount of water excreted through the kidneys, skin, and lungs per unit of body surface is far greater than in adults. In pathological conditions causing hypo-osmolar dehydration, thirst should be quenched by drinking salted water to compensate not only for the water loss but the loss of electrolytes as well. Treatment consists in removing the primary cause of dehydration.

G. A. DROZDOVA

dehydration

The removal of water vapor from air by the use of absorbing or adsorbing materials.
References in periodicals archive ?
(10) Specific gravity values were categorized as euhydration (USG<1.02) or hypohydration (USG [greater than or equal to] 1.02).
Physiological consequences of hypohydration: exercise performance and thermoregulation.
Furthermore, it may give rise to misleading results since, for instance, a significant loss of BM may be observed without an effective hypohydration resulting (Cheuvront and Kenefick, 2017; Maughan et al., 2007).
Hypohydration during exercise in children: effect on thirst, drink preferences, and rehydration.
High skin temperature and hypohydration impair aerobic performance.
Skin temperature modifies the impact of hypohydration on aerobic performance.
For the W+ trials, caffeine ingestion caused a significant difference (p=0.02) in hypohydration (Table 1).
A sample of urine was separated for urine specific gravity (USG) analysis (euhydration <1.020 and hypohydration [greater than or equal to] 1.020 [3]) by refractom etry (Refractometer Hand-Held, ATAGO 2722-E04) and the color was determined according to Armstrong et al.
Nutrition: training on low carbohydrate; galactose vs other carbs and caffeine; milk protein, amino acids and cherry juice for recovery; colostrum for training; vitamin C and fish oil for asthmatics; echinacea stimulates EPO; caffeine for team-sport and tennis performance; effects of mild hypohydration. Performance Genes: minor findings.
Hypohydration was common for the first two days (n = 21, SG of 1.027 [+ or -] 0.009 and 1.033 [+ or -] 0.018 for days 1 and 2 respectively), when nearly 50% of soldiers had highly concentrated urines (i.e.
(1985) Plasma hormonal responses at graded hypohydration levels during exercise-heat stress.
The urinary osmolality use indicated hypohydration in 78% of the athletes.