Why red blood cells swell or shrink in blood?

Red blood cells swell or shrink in response to changes in the osmotic pressure of their surrounding environment. Osmotic pressure is the pressure exerted by a solution to prevent the passage of water across a semipermeable membrane. It is influenced by the concentration of solute particles within the solution.

Swelling (Hemolysis)

If red blood cells are placed in a hypotonic solution (a solution with lower solute concentration compared to the cell's interior), water moves into the cell due to the higher osmotic pressure inside the cell. As water enters, the cell swells and may eventually burst in a process called hemolysis.

Shrinking (Crenation)

On the other hand, when red blood cells are placed in a hypertonic solution (a solution with higher solute concentration compared to the cell's interior), water moves out of the cell due to the higher osmotic pressure outside the cell. This water loss causes the cell to shrink, leading to a crenated or wrinkled appearance.

These changes in red blood cell shape and size can affect their function. Hemolysis can cause the premature destruction of red blood cells and lead to anemia. Crenation, while a reversible process, can alter the deformability of red blood cells, affecting their ability to pass through narrow capillaries and deliver oxygen efficiently to tissues.

Maintaining the appropriate osmotic balance in the bloodstream is crucial to preserving the integrity and functionality of red blood cells.