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| | ==Overview== |
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| ==Overview==
| | Hypomagnesemia is an [[electrolyte disturbance]] in which there is an abnormally low level of [[magnesium]] in the blood. Usually a serum level less than 0.7 mmol/l is used as reference. It must be noted that hypomagnesemia is not equal to magnesium deficiency. Hypomagnesemia can be present without [[magnesium deficiency (medicine)|magnesium deficiency]] and vice versa. |
| The prefix hypo- means low (contrast with hyper-, meaning high). The middle magnes refers to magnesium. The end portion of the word, -emia, means 'in the blood' (note, however, that hypomagnesemia is usually indicative of a systemic magnesium deficit).
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| Thus, '''Hypomagnesemia''' is an [[electrolyte disturbance]] in which there is an abnormally low level of [[magnesium]] in the blood. Usually a serum level less than 0.7 mmol/l is used as reference. It must be noted that hypomagnesemia is not equal to magnesium deficiency. Hypomagnesemia can be present without [[magnesium deficiency (medicine)|magnesium deficiency]] and vice versa.
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| It may result from a number of conditions including inadequate intake of magnesium, chronic [[diarrhea]], [[malabsorption]], [[alcoholism]], [[chronic stress]], [[diuretic]] use and other disorders. | | It may result from a number of conditions including inadequate intake of magnesium, chronic [[diarrhea]], [[malabsorption]], [[alcoholism]], [[chronic stress]], [[diuretic]] use and other disorders. |
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| ==Homeostasis== | | ==Historical Perspective== |
| The body contains 21-28 grams of magnesium (1 mmol=2mEq=24.6 mg). Of this, 53% is located in [[bone]], 19% in non-muscular tissue, and 1% in [[extracellular fluid]]. For this reason, blood levels of magnesium are not an adequate means of establishing the total amount of available magnesium. | | The prefix hypo- means low (contrast with hyper-, meaning high). The middle magnes refers to magnesium. The end portion of the word, -emia, means 'in the blood' (note, however, that hypomagnesemia is usually indicative of a systemic magnesium deficit). |
| Most of the serum magnesium is bound to chelators, (i.e. [[Adenosine triphosphate|ATP]], [[Adenosine diphosphate|ADP]], [[protein]]s and [[citrate]]). Roughly 33% is bound to proteins, and 5-10% is not bound. This "free" magnesium is essential in regulating intracellular magnesium. Normal plasma Mg is 1.7-2.3 mg/dl (0.69-0.94 mmol/l). Of this 60% is free, 33% is bound to proteins, and less than 7% is bound to citrate, [[bicarbonate]] and [[phosphate]].
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| Magnesium is abundant in nature. It can be found in green vegetables, [[chlorophyll]], coca-derivatives, nuts, wheat, seafood, and meat. It is resorbed through the [[small intestine]], and to a lesser degree in the [[Colon (anatomy)|colon]]. The [[rectum]] and [[sigmoid colon]] can absorb magnesium. [[Hypermagnesemia]] has been reported after enemas containing magnesium. Forty percent of dietary magnesium is absorbed. Hypomagnesemia stimulates and hypermagnesemia inhibits this absorption.
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| The [[kidney]]s regulate the serum magnesium. About 2400 mg of magnesium passes through the kidneys, of which 5% (120 mg) is excreted through [[urine]]. The [[loop of Henle]] is the major site for Mg-homeostasis and 60% is resorbed. | |
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| Magnesium homeostasis comprises three systems: kidney, small intestine, and bone. In the acute phase of magnesium deficiency there is an increase in absorption in the distal small intestine and tubular resorption in the kidneys. When this condition persists serum magnesium drops and is corrected with magnesium from bone tissue. The level of intracellular magnesium is controlled through the reservoir in bone tissue.
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| ==Metabolism==
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| Magnesium is a cofactor in more than 300 [[enzyme]] regulated reactions. Most importantly forming and using ATP, i.e. kinase. There is a direct effect on sodium- (Na), potassium- (K) and calcium (Ca)channels. It has several effects:
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| *Potassium channels are inhibited by magnesium. Hypomagnesemia results in increased [[efflux]] of intracellular Mg. The cell loses potassium which then is excreted by the kidneys, resulting in [[hypokalemia]].
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| *Release of calcium from the [[sarcoplasmic reticulum]] is inhibited by magnesium. Low levels of magnesium stimulate the release of calcium and thereby an intracellular level of calcium. This effect similar to calcium inhibitors makes it "nature's [[Calcium channel blocker|calcium inhibitor]]." Lack of magnesium inhibits the release of [[parathyroid hormone]], which can also result in [[hypocalcemia]]. Furthermore, it makes skeletal and muscle receptors less sensitive to parathyroid hormone.
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| *Through relaxation of bronchial smooth muscle it causes [[bronchodilation]].
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| *The neurological effects are:
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| **reducing electrical excitation
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| **blocking release of [[acetylcholine]]
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| **blocking N-methyl-D-aspartate, an excitatory [[neurotransmitter]] of the central nervous system
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| ==References== | | ==References== |
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| {{Reflist|2}} | | {{Reflist|2}} |
| [[Category:Needs content]]
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| [[Category:Electrolyte disturbance]] | | [[Category:Electrolyte disturbance]] |
| [[Category:Intensive care medicine]] | | [[Category:Intensive care medicine]] |