THE ELECTROLYTE: MAGNESIUM
General information
Magnesium (Mg) is a major cation (cat ion) in the intracellular fluid (ICF), closely related to calcium (Ca) and phosphorus (P). Intracellular fluid is the blood in the red blood cells. ECF, or extracellular fluid is the plasma in red blood cells. Because their cells allow different substances to permeate, the ICF and ECF have different electrolyte concentrations.
About 60% of magnesium is contained in bone.
A normal diet supplies approximately 25 milequillevent (mEq) of Mg daily; of this amount, 10 mEq is absorbed trough the small bowel, 10 mEq is excreted in urine, and the ramainder is excreted in feces.
Normal serum Mg level ranges from 1.5 to 2.5 mEq/liter, with 33% bound to protein and the ramainder existing as free cations.
Normal Mg concentration in the ICF is 40 mEq/liter.
Functions:
Activates intracellular enzymes and acts in carbohydrate and protein metabolism.
Acts on the mtoneural junction, affecting neuromuscular irritability and contractility of cardiac and skeletal muscle.
Affects peripheral vasodilation, resulting in changes in blood pressure and cardiac output
Facilitates transport of Na and K across cell membranes
Influences intracellular Ca level through its effect of PTH secretion
Regulation:
Control of Mg is not clearly understook
Factors that influence Ca and K balance seem to act on Mg as well
Sighn and symptoms of Mg imbalance--particularly hypomagnesemia--mimic those of Ca imbalance, which may interfere with diagnosis and treatment of Mg imbalance
The kidneys can conserve Mg efficiently, restricting losses to 1 mEq/day if necessary; however, excessive Mg excretion can result from diuretic use.
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