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