A cartoon representation of wall-less and walled cell responses to osmotic downshifts. The wall-less cell (top) behaves like an osmometer with release valves: it swells first and opens osmolyte release channels and partially returns to its initial state, which is close to equilibrium with the new more dilute medium. Shrinkage is not expected. The walled cell maintains its volume by generating turgor pressure that counters the restoring force of the elastic cell wall. Swelling and opening of mechanosensitive channels will release osmolytes and water, but if the channels remain open for too long, the compression may extrude water and shrink the cell beyond its normal volume. Channels that sense the increasing cytoplasmic crowding will inactivate and prevent over-draining of the cytoplasm.