Fluid & Electrolyte Q 19

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The chief anion in the intracellular fluid (ICF) is:

  

    A. Phosphorus

    B. Potassium

    C. Sodium

    D. Chloride

    

    

Correct Answer: A. Phosphorus

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Phosphorus is the major ICF cation. Phosphorus is an extracellular fluid cation. Eighty-five percent of the total body phosphorus is in the bones and teeth in the form of hydroxyapatite; the soft tissues contain the remaining 15%. Phosphate plays a crucial role in metabolic pathways.

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Option B: Potassium is a cation. Potassium is an essential mineral constituent of the human body and is the chief cation found within the intracellular fluid of all cells. The chief indication for potassium administration is potassium deficiency or hypokalemia, a condition in which serum potassium level falls below a critical range.

Option C: Sodium is a cation. Sodium, which is an osmotically active anion, is one of the most important electrolytes in the extracellular fluid. It is responsible for maintaining the extracellular fluid volume, and also for regulation of the membrane potential of cells. Sodium is exchanged along with potassium across cell membranes as part of active transport.

Option D: Chloride is the chief anion found in the ECF. Chloride is an anion found predominantly in the extracellular fluid. The kidneys predominantly regulate serum chloride levels. Most of the chloride, which is filtered by the glomerulus, is reabsorbed by both proximal and distal tubules (majorly by proximal tubule) by both active and passive transport.

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