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Regulation of magnesium balance

Author
Alan S L Yu, MB, BChir
Section Editor
Stanley Goldfarb, MD
Deputy Editor
Albert Q Lam, MD

INTRODUCTION

Magnesium balance, like that of other ions, is a function of intake and excretion. The average daily magnesium intake is 360 mg (15 mmol). Approximately one-third of this magnesium is absorbed, principally in the small bowel through both a saturable transport system (presumably mediated by a channel encoded by the TRPM6 gene) and passive diffusion. (See "Causes of hypomagnesemia".)

Two other processes occur in the gut: the secretion of approximately 40 mg (1.7 mmol) in intestinal secretions, and the absorption of another 20 mg (0.8 mmol) in the large bowel. In the healthy adult, there is no net gain or loss of magnesium from bone so that balance is achieved by the urinary excretion of the approximately 100 mg (4.1 mmol) that is absorbed. Changes in intake are balanced by changes in urinary magnesium reabsorption, principally in the loop of Henle and the distal tubule.

UNITS OF MEASUREMENT

Before discussing the factors responsible for the regulation of magnesium balance, it is useful to review the different units that may be used to measure the plasma (or serum) magnesium concentration. Laboratories in the United States usually report the results in units of meq/L or mg/dL, while other countries primarily use mmol/L. The relationship among these units can be expressed by the following equations:

 mmol/L  =  [mg/dL  x  10]  ÷  mol wt

 meq/L  =  mmol/L  x  valence

       

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Literature review current through: Nov 2016. | This topic last updated: Mon Feb 01 00:00:00 GMT+00:00 2016.
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