Magnesium performs all of the following functions except:
A. Contributing to vasoconstriction.
B. Assisting in cardiac muscle contraction.
C. Facilitating sodium transport.
D. Assisting in protein metabolism.
Correct Answer: A. Contributing to vasoconstriction.
Magnesium contributes to vasodilation, not vasoconstriction. Magnesium plays a vital role in over 300 reactions involving metabolism. It is involved with hormone receptor binding, muscle contraction, neural activity, neurotransmitter release, vasomotor tone, and cardiac excitability.
Option B: Magnesium acts as a natural calcium channel blocker, and it is a cofactor of the Na-K-ATP pump. Magnesium helps control atrioventricular node conduction. Therefore, hypomagnesemia can cause myocardial excitability resulting in arrhythmias such as ventricular tachycardia and torsades de pointes.
Option C: It is necessary for the active transport of potassium and calcium across the cell membrane. ATP is dependent on magnesium for proper functioning. Roughly 50% of magnesium is located within the bone, 25% is within the muscle, and the remainder is in soft tissue, serum, and red blood cells (RBC).
Option D: The intestine, bone, and kidney maintain magnesium homeostasis. Similar to calcium, magnesium is absorbed via the intestine, stored in the bone, excreted via the kidneys. Absorption of magnesium is inversely proportional to the concentration within the body; if there are low magnesium levels within the body, more magnesium will be absorbed.
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