Hypertonic Solution Definition

A solution is classified as hypertonic when the concentration of solutes dissolved in it is greater than the concentration of solutes inside the cells it surrounds. This is specifically measured by comparing osmolarity.

Key characteristics:

• Higher Osmolarity: The osmolarity of the external solution is significantly higher than that of the cell's cytosol. Mathematically, if $O_{solution}$ represents the osmolarity of the solution and $O_{cytosol}$ represents the osmolarity of the cytosol, a solution is hypertonic if $O_{solution} > O_{cytosol}$.
• Water Movement: Due to the higher solute concentration outside the cell, water molecules tend to move across the semipermeable cell membrane from the area of lower solute concentration (inside the cell) to the area of higher solute concentration (outside the cell) via osmosis.
• Cellular Effect: This net movement of water out of the cell typically causes the cell to shrink or crenate.

Therefore, a hypertonic solution is defined by its higher osmolarity compared to the cell's cytosol.