Dehydration (redirected from hypernatremic dehydration)

dehydration

Method of food preservation in which moisture (primarily water) is removed. Dehydration inhibits the growth of microorganisms and often reduces the bulk of food. It is an ancient practice, used by prehistoric peoples in sun-drying seeds, by North American Indians in sun-drying meat strips, and by the Japanese in drying fish and rice. It was used to prepare troop rations in World War II, and in recent decades campers and relief agencies have discovered its advantages. Commercial dehydration equipment includes tunnel dryers, kilns, and vacuum dryers. A combination of dehydration and freezing is used in the process of freeze-drying, whereby solid food remains frozen while its liquid escapes as vapour. The dairy industry is one of the largest producers of dehydrated foods, including whole milk, skim milk, and eggs.

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dehydration

Loss of water, almost always along with salt, from the body, caused by restricted water intake or excessive water loss. Early symptoms of water deprivation are thirst, decreased saliva, and impaired swallowing. (When more electrolytes than water are lost, osmosis pulls water into cells, and there is no thirst.) Later, tissues shrink, including the skin and eyes. Mild fever rises as plasma volume and cardiac output decrease, and perspiration decreases or stops, greatly reducing heat loss. Urine output falls, and the kidneys cannot filter wastes from the blood. Irreversible shock can occur at this point. The cause of dehydration is treated first; then water and electrolytes must be given in the correct proportions.

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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.

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dehydration

The removal of water vapor from air by the use of absorbing or adsorbing materials.

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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

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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