Fluid & Electrolyte Q 23

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The major cation in the ICF is:

  

    A. Potassium

    B. Sodium

    C. Phosphorus

    D. Magnesium

    

    

Correct Answer: A. Potassium

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Potassium is the major ICF cation. Potassium is mainly an intracellular ion. The sodium-potassium adenosine triphosphatase pump has the primary responsibility for regulating the homeostasis between sodium and potassium, which pumps out sodium in exchange for potassium, which moves into the cells.

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Option B: Sodium is the major ECF 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 C: Phosphorus is the major ICF anion. 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. It is a component of many metabolic intermediates and, most importantly of adenosine triphosphate(ATPs) and nucleotides.

Option D: Magnesium is the second-most abundant cation in the ICF. Magnesium is an intracellular cation. Magnesium is mainly involved in ATP metabolism, contraction and relaxation of muscles, proper neurological functioning, and neurotransmitter release. When muscle contracts, calcium re-uptake by the calcium-activated ATPase of the sarcoplasmic reticulum is brought about by magnesium.

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