With dehydration, which fluid compartment's volume is lost and it occurs over time?

• A. Intracellular fluid, over time
• B. Extracellular fluid, immediately
• C. Intracellular fluid, immediately
• D. Extracellular fluid, over time

Answer: (A)

When dehydration occurs, the body's osmolality rises because water is lost. Water moves by osmosis from areas of lower osmolality to higher osmolality to restore balance. This redistribution causes water to leave cells and enter the extracellular space, so the intracellular fluid volume gradually decreases over time. The change in the intracellular compartment isn’t immediate—the ongoing osmotic shift reduces intracellular water progressively, making the intracellular fluid the one that diminishes as dehydration progresses.