An isotonic solution is one wherein the solute concentration across the semipermeable membrane is the same resulting in an equilibrium state.
They do not shrink or swell in an isotonic saline solution, i.e., 0.9% w/v solution of sodium chloride
Hypertonic solution: A solution that contains more dissolved particles (such as salt and other electrolytes) than is found in normal cells and blood.
Now, let’s suppose RBCs are placed in a solution with a sodium chloride concentration of 2% w/v. The sodium chloride concentration of 2% w/v is greater than the RBC’s sodium content and hence the solution is hypertonic. This will result in shrinkage of the RBCs known as crenation
When a solution has a lower solute concentration than the solution present across the semipermeable membrane, it is known as a hypotonic solution. As a result, when a cell is placed in a hypotonic solution, an osmotic pressure gradient forces the solvent to move into the cell in order to attain equal solute
In another situation, let’s suppose RBCs are placed in a solution with a sodium chloride concentration of 0.1 % w/v. The sodium chloride concentration of 0.1% w/v is less than the RBC’s sodium content and hence hypotonic saline. This will result in swelling and eventually bursting of the RBCs which will result in the release of hemoglobin. This is known as hemolysis which is a very dangerous situation.
