What happens when water is lost but electrolytes are retained?

When water is lost but electrolytes are retained, the balance of solutes and the concentration gradient between the extracellular fluid (ECF) and intracellular fluid (ICF) changes significantly. The retention of electrolytes creates a hypertonic environment in the ECF relative to the ICF. This means that the concentration of solutes (like electrolytes) in the ECF increases compared to the ICF.

In response to this hypertonic state, water naturally moves from areas of lower solute concentration (the ICF) to areas of higher solute concentration (the ECF) through a process known as osmosis. This movement helps to equalize the concentration of solutes on both sides of the cell membrane.

Thus, the correct answer indicates that osmosis drives water from the intracellular fluid to the extracellular fluid, effectively balancing the osmotic pressure due to the loss of water and retention of electrolytes. This physiological response is critical in the maintenance of homeostasis within the body.