If a person is severely dehydrated, their extracellular fluid becomes hypertonic relative to the intracellular fluid. This hypertonic extracellular environment causes water to move out of the cells by osmosis in an attempt to balance solute concentrations across the cell membrane. As a result, the person's cells will lose water and shrink (cellular dehydration or shrinkage)
. This shrinkage occurs because water moves from the area of lower solute concentration inside the cells to the area of higher solute concentration outside the cells. The loss of intracellular water can impair cellular functions and may lead to symptoms such as confusion, seizures, and other neurological effects due to brain cell shrinkage in severe dehydration
