Which statement correctly lists the three body water compartments and identifies the majority compartment in a typical 70 kg adult?

• A. Intravascular 7.1%; Interstitial 38%; Intracellular 55% (majority)
• B. Intravascular 7.1%; Intracellular 60%; Interstitial 33%
• C. Intracellular 50%; Interstitial 40%; Intravascular 10% (majority)
• D. Interstitial 38%; Intravascular 7.1%; Intracellular 50% (majority)

Answer: (A)

The key idea is that body water is divided into intracellular fluid (inside cells) and extracellular fluid (outside cells), with the extracellular portion further split into plasma (intravascular) and interstitial fluid. In a typical 70 kg adult, the largest share of body water is inside cells, making intracellular fluid the majority. The numbers shown reflect that distribution: intravascular fluid is a small portion, about 7.1% of body weight; interstitial fluid is a substantial portion, about 38%; and intracellular fluid makes up the largest share, about 55%. Because intracellular fluid is the biggest compartment, it is identified as the majority. This aligns with the overall pattern that most body water is intracellular, while extracellular water (plasma plus interstitial) is smaller, with plasma being the smallest component. Shifts between these compartments occur with osmosis and fluid therapy, which is why understanding this distribution matters clinically. The other sets either place the larger share in a nonmajor compartment or misstate the relative sizes, so they don’t fit the typical pattern where intracellular fluid is the dominant reservoir.