Which statement about dehydration and osmolality is true?

Which statement about dehydration and osmolality is true?

• A. Water loss increases osmolality
• B. Osmolality fluctuates unpredictably with water loss
• C. Osmolality does not change with water loss
• D. Water loss decreases osmolality

Answer: (A)

Loss of water without a proportional loss of solutes makes the remaining body fluids more concentrated. Osmolality measures solute concentration, so when water is removed, the same amount of solutes is in less fluid, and osmolality rises. This rise in osmolality stimulates thirst and the release of antidiuretic hormone to conserve water. So, water loss increases osmolality. If water and solutes were lost in the same proportion, osmolality might stay the same; losing more solutes than water could lower osmolality, but simple water loss elevates it.

Loss of water without a proportional loss of solutes makes the remaining body fluids more concentrated. Osmolality measures solute concentration, so when water is removed, the same amount of solutes is in less fluid, and osmolality rises. This rise in osmolality stimulates thirst and the release of antidiuretic hormone to conserve water. So, water loss increases osmolality. If water and solutes were lost in the same proportion, osmolality might stay the same; losing more solutes than water could lower osmolality, but simple water loss elevates it.