Pathophysiology
Clinical meaning
Magnesium is the fourth most abundant cation in the body and the second most abundant intracellular cation after potassium. Approximately 50 to 60 percent of total body magnesium is stored in bone, 39 percent resides within cells (primarily skeletal muscle and soft tissue), and only about 1 percent circulates in the blood. The normal serum magnesium level ranges from 0.70 to 1.05 mmol/L (1.7 to 2.1 mg/dL in some references). Because such a small fraction of total body magnesium is measurable in serum, a patient can have significant intracellular magnesium depletion while still maintaining a serum level that appears low-normal. Magnesium serves as a cofactor for more than 300 enzymatic reactions in the body, including those involved in protein synthesis, neuromuscular function, blood glucose regulation, and blood pressure control. It plays a critical role in maintaining the stability of cell membranes and is essential for the proper function of the sodium-potassium ATPase pump, which maintains the electrochemical gradient across cell membranes. In the neuromuscular system, magnesium acts as a natural calcium channel blocker at the neuromuscular junction, competing with calcium...