Hypertonic crystalloids produce what effect on cell volume when placed in a solution with higher osmolarity than the extracellular fluid?

• A. Increases
• B. Decreases
• C. No change
• D. Varies

Answer: (B)

Water moves across cell membranes by osmosis toward the side with higher solute concentration. If you place a cell in a solution with higher osmolarity than the cell’s interior, water leaves the cell to balance the concentrations, causing the cell to shrink and its volume to decrease. Hypertonic crystalloids create that higher extracellular osmolarity, pulling water out of cells. If the outside were isotonic, there’d be no net water movement; if it were hypotonic, water would enter the cell and its volume would increase.