Which plasma electrolyte has the most narrow reference range and is MOST strictly regulated by the body?

Which plasma electrolyte has the most narrow reference range and is MOST strictly regulated by the body?

• A. Sodium
• B. Magnesium
• C. Calcium
• D. Potassium

Answer: (D)

Potassium is kept in plasma at a very tight range because it sets the resting membrane potential for all excitable cells. Small changes in extracellular potassium have big effects on the excitability of cardiac and nerve tissue, so the body enforces a narrow window to prevent dangerous effects like arrhythmias or muscle weakness. Regulation is rapid and precise: the kidneys adjust excretion in the distal nephron under aldosterone control, and shifts between inside- and outside-of-cell compartments are driven by Na-K ATPase activity, insulin, and catecholamines; acid-base balance also moves potassium between compartments. While other electrolytes are regulated, none have to be maintained with as much precision or as directly tied to essential electrical activity as potassium, making it the electrolyte with the most narrow reference range.

Potassium is kept in plasma at a very tight range because it sets the resting membrane potential for all excitable cells. Small changes in extracellular potassium have big effects on the excitability of cardiac and nerve tissue, so the body enforces a narrow window to prevent dangerous effects like arrhythmias or muscle weakness. Regulation is rapid and precise: the kidneys adjust excretion in the distal nephron under aldosterone control, and shifts between inside- and outside-of-cell compartments are driven by Na-K ATPase activity, insulin, and catecholamines; acid-base balance also moves potassium between compartments. While other electrolytes are regulated, none have to be maintained with as much precision or as directly tied to essential electrical activity as potassium, making it the electrolyte with the most narrow reference range.