How does osmolarity affect cells?
In fact, an osmotic pressure is established that is proportional to the difference between external and internal osmolarities and this unbalanced pressure can cause a mechanical stress to the cell membrane.
From the molecular point of view, water molecules move across a membrane from a lower osmolarity to a higher osmolarity. In other words, water moves from the dilute side to the concentrated side.
The dilute side loses water and becomes more concentrated. The concentrated side gains water to become more dilute.
Cell survival depends on balancing water uptake and loss. Cells can burst if they take on too much water, or collapse if they lose too much.
Cell membranes in general are permeable to water. Thus, the osmolality of the extracellular fluid (ECF) is approximately equal to that of the intracellular fluid (ICF).
This is important, because it shows that changes in ECF osmolarity have a great effect on ICF osmolarity.
If the osmolarity of the ECF becomes too low, water will fill the cells. This increases their volume and may lead to their rupture (cytolysis).
If the osmolarity of the ECF becomes too high water will leave the cells. This decreases volume and may lead to their shrinking (crenation).