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| {{CMG}}
| | #redirect:[[Electrolyte disturbance]] |
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| '''Associate Editor-In-Chief:''' {{CZ}}
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| ==Overview==
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| {{SI}}
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| An '''electrolyte''' is a substance containing free [[ion]]s that behaves as an electrically conductive medium. Because they generally consist of ions in solution, electrolytes are also known as '''ionic solutions''', but molten electrolytes and solid electrolytes are also possible. They are sometimes referred to in abbreviated jargon as '''lytes'''.
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| == Principles ==
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| Electrolytes commonly exist as solutions of [[acid]]s, [[base (chemistry)|base]]s or [[salt]]s. Furthermore, some [[gas]]es may act as electrolytes under conditions of high temperature or low pressure. Electrolyte solutions can also result from the dissolution of some biological (e.g. [[DNA]], [[Peptide|polypeptides]]) and synthetic polymers (e.g. [[Sodium polystyrene sulfonate|poly(styrene sulfonate)]], termed polyelectrolytes, which contain multiple charged moieties.
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| Electrolyte solutions are normally formed when a [[salt]] is placed into a [[solvent]] such as [[water]] and the individual components dissociate due to the thermodynamic interactions between solvent and [[solute]] molecules, in a process called [[solvation]]. For example, when [[Sodium chloride|table salt]], NaCl, is placed in water, the following occurs:<br />
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| :NaCl(s) → Na<sup>+</sup> + Cl<sup>−</sup>
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| In simple terms, the electrolyte is a material that dissolves in water to give a solution that conducts an electric current.
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| An electrolyte in a solution may be described as ''concentrated'' if it has a high [[concentration]] of ions, or ''dilute'' if it has a low concentration. If a high ''proportion'' of the [[solute]] dissociates to form free ions, the electrolyte is ''strong''; if most of the solute does not dissociate, the electrolyte is ''weak''. The properties of electrolytes may be exploited using [[electrolysis]] to extract constituent [[chemical element|elements]] and [[Chemical compound|compounds]] contained within the solution.
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| == Physiological importance ==
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| In [[physiology]], the primary ions of electrolytes are [[sodium]] (Na<sup>+</sup>), [[potassium]] (K<sup>+</sup>), [[calcium]] (Ca<sup>2+</sup>), [[magnesium]] (Mg<sup>2+</sup>), [[chloride]] (Cl<sup>-</sup>), [[phosphate]] (PO<sub>4</sub><sup>3-</sup>), and [[hydrogen carbonate]] (HCO<sub>3</sub><sup>-</sup>). The electric charge symbols of plus (+) and minus (-) indicate that the substance in question is ionic in nature and has an imbalanced distribution of electrons. This is the result of chemical dissociation.
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| All higher lifeforms require a subtle and complex electrolyte balance between the [[intracellular]] and [[extracellular]] milieu. In particular, the maintenance of precise [[osmotic]] [[ion gradient|gradient]]s of electrolytes is important. Such gradients affect and regulate the hydration of the body, [[blood]] [[pH]], and are critical for [[nerve]] and [[muscle]] function.
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| Both muscle tissue and neurons are considered electric tissues of the body. Muscles and neurons are activated by electrolyte activity between the [[extracellular fluid]] or interstitial fluid, and [[intracellular fluid]]. Electrolytes may enter or leave the cell membrane through specialized protein structures embedded in the [[plasma membrane]] called [[ion channels]]. For example, [[muscle contraction]] is dependent upon the presence of calcium (Ca<sup>2+</sup>), sodium (Na<sup>+</sup>), and potassium (K<sup>+</sup>). Without sufficient levels of these key electrolytes, muscle weakness or severe muscle contractions may occur.
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| Electrolyte balance is maintained by oral, or in emergencies, intravenous (IV) intake of electrolyte-containing substances, and is regulated by [[hormone]]s, generally with the [[kidney]]s flushing out excess levels. In humans, electrolyte [[homeostasis]] is regulated by hormones such as [[antidiuretic hormone]], [[aldosterone]] and [[parathyroid hormone]]. Serious [[electrolyte disturbance]]s, such as [[dehydration]] and [[water poisoning|overhydration]], may lead to cardiac and neurological complications and, unless they are rapidly resolved, will result in a [[medical emergency]]. | |
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| === Measurement ===
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| Measurement of electrolytes is a commonly performed diagnostic procedure, performed via [[blood test]]ing with [[ion selective electrode]]s or [[urinalysis]] by [[medical technologist]]s. The interpretation of these values is somewhat meaningless without analysis of the [[medical history|clinical history]] and is often impossible without parallel measurement of [[renal function]]. Electrolytes measured most often are sodium and potassium. Chloride levels are rarely measured except for [[arterial blood gas]] interpretation since they are inherently linked to sodium levels. One important test conducted on urine is the [[specific gravity]] test to determine the occurrence of [[electrolyte imbalance]].
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| === Sports drinks ===
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| Electrolytes are commonly found in [[sports drink]]s. In [[oral rehydration therapy]], electrolyte drinks containing sodium and potassium salts replenish the body's [[water]] and electrolyte levels after [[dehydration]] caused by [[exercise]], [[diaphoresis]], [[diarrhea]], [[vomiting]] or [[starvation]]. Giving pure water to such a person is not the best way to restore fluid levels because it dilutes the salts inside the body's cells and interferes with their chemical functions. This can lead to [[water intoxication]].
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| Sports drinks such as Gatorade, Powerade, or [[Lucozade]] are electrolyte drinks with large amounts of added [[carbohydrate]]s, such as [[glucose]], to provide energy. The drinks commonly sold to the public are [[isotonic]] (with [[osmolality]] close to that of blood), with [[hypotonic]] (with a lower osmolality) and [[hypertonic]] (with a higher osmolality) varieties available to athletes, depending on their nutritional needs.[http://www.disen.org/nutrition/pages-to-edit/fluids.htm]
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| It is unnecessary to replace losses of sodium, potassium and other electrolytes during exercise since it is unlikely that a significant depletion the body's stores of these minerals will occur during normal training. However, in extreme exercising conditions over 5 or 6 hours (an Ironman or ultramarathon, for example) the consumption of a complex sports drink with electrolytes is recommended. Athletes who do not consume electrolytes under these conditions risk overhydration (or hyponatremia). [http://sportsmedicine.about.com/cs/hydration/a/aa041103a.htm]
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| Because sports drinks typically contain very high levels of [[sugar]], they are not recommended for regular use by children. Rather, specially-formulated pediatric electrolyte solutions are recommended. Sports drinks are also not appropriate for replacing the fluid lost during diarrhea. The role of sports drinks is to inhibit electrolyte loss but are insufficient to restore balance once it occurs. Medicinal rehydration sachets and drinks are available to replace the key electrolyte ions lost. Dentists recommend that regular consumers of sports drinks observe precautions against [[tooth decay]].
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| Electrolyte and sports drinks can be home-made by using the correct proportions of sugar, salt and water. [http://www.webmd.com/hw/health_guide_atoz/str2254.asp?navbar=hw86827]
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| == Electrochemistry ==
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| {{Main|electrolysis}}
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| When two [[electrode]]s are placed in an electrolyte and a [[voltage]] is applied, the electrolyte will conduct electricity. Lone [[electron]]s normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the [[cathode]] consuming electrons from the cathode, and another reaction occurs at the [[anode]] producing electrons to be taken up by the anode. As a result, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge develops around the anode. The ions in the electrolyte move to neutralize these charges so that the reactions can continue and the electrons can keep flowing.
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| For example, in a dilute solution of ordinary salt ([[sodium chloride]], NaCl) in water, the cathode reaction will be
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| :2H<sub>2</sub>O + 2e<sup>−</sup> → 2OH<sup>−</sup> + H<sub>2</sub>
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| and [[hydrogen]] gas will bubble up; the anode reaction is
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| :2H<sub>2</sub>O → O<sub>2</sub> + 4H<sup>+</sup> + 4e<sup>−</sup>
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| and [[oxygen]] gas will be liberated. The positively charged sodium ions Na<sup>+</sup> will move towards the cathode neutralizing the negative charge of OH<sup>−</sup> there, and the negatively charged chlorine ions Cl<sup>−</sup> will move towards the anode neutralizing the positive charge of H<sup>+</sup> there. Without the ions from the electrolyte, the charges around the electrode would slow down continued electron flow; [[diffusion]] of H<sup>+</sup> and OH<sup>−</sup> through water to the other electrode takes longer than movement of the much more prevalent salt ions.
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| In other systems, the electrode reactions can involve the metals of the electrodes as well as the ions of the electrolyte.
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| Electrolytic conductors are used in electronic devices where the chemical reaction at a metal/electrolyte interface yields useful effects.
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| *In batteries, two [[metal]]s with different electron affinities are used as electrodes; electrons flow from one electrode to the other outside of the battery, while inside the battery the circuit is closed by the electrolyte's ions. Here the electrode reactions slowly use up the chemical energy stored in the electrolyte.
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| *In some fuel cells, a solid electrolyte or proton conductor connects the plates electrically while keeping the hydrogen and oxygen fuel gases separated.
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| *In electroplating tanks, the electrolyte simultaneously deposits metal onto the object to be plated, and electrically connects that object in the circuit.
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| *In operation-hours gauges, two thin columns of [[mercury (element)|mercury]] are separated by a small electrolyte-filled gap, and, as charge is passed through the device, the metal dissolves on one side and plates out on the other, causing the visible gap to slowly move along.
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| *In electrolytic capacitors the chemical effect is used to produce an extremely thin 'dielectric' or insulating coating, while the electrolyte layer behaves as one capacitor plate.
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| *In some hygrometers the humidity of air is sensed by measuring the conductivity of a nearly dry electrolyte.
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| *Hot, softened glass is an electrolytic conductor, and some glass manufacturers keep the glass molten by passing a large electric current through it.
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| ==See also==
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| *[[Strong electrolyte]]
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| [[Category:Blood tests]]
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| [[Category:Urine tests]]
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| [[Category:Physiology]]
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| [[Category:Nephrology]]
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