Advanced Patient Assessment Practice Exam

Which of the following is considered the major cation of the extracellular fluid?

1. Sodium

2. Chloride

3. Potassium

4. Calcium

The correct answer is: Sodium

Sodium is recognized as the major cation of the extracellular fluid due to its significant role in maintaining osmotic pressure and fluid balance in the body. It is primarily found in the interstitial fluid and plasma, accounting for roughly 90% of the cations present in extracellular compartments. Sodium ions are crucial for the generation of action potentials in neurons and muscle cells, facilitating nerve impulses and muscle contractions. The other options do play important roles in the body but do not serve as the predominant cation in extracellular fluid. For example, chloride is an anion that often accompanies sodium to help maintain electrical neutrality across membranes. Potassium is the primary cation within cells, essential for cellular functions but is predominantly found in the intracellular fluid. Calcium, while vital for various physiological functions such as muscle contraction and neurotransmitter release, is present in much lower concentrations in extracellular fluid compared to sodium. Thus, sodium's abundance and functional significance solidify its position as the major cation of extracellular fluid.