Outline the distribution, clearance and physiologic functions of magnesium in the body.

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College Answer

Insufficient breadth and depth of knowledge limited candidates’ performance to this 
question. Candidates were expected to mention normal plasma (0.7 – 1.1 mmol/l) and 
intracellular (20mmol/l) levels, distribution (approximately 50% of total body magnesium is 
in bone & 20% in skeletal muscles), clearance (almost solely renal, approaches GFR, renal 
threshold set at just above normal serum Mg concentration, below which get almost 
complete reabsorption), activity (e.g. co-factor in metabolism), effects on muscles (reduces 
muscle excitability, inhibits excitation-contraction coupling, reduced contractility / weakness 
/ depressed reflexes), effects on nerves (e.g. reduces nerve excitability, blocks NMDA 
receptors), systemic and coronary vasodilation and inhibits platelet function.