Hypertonic Solution or HypertonicictyWhen the osmotic pressure of the solution outside the blood cells in higher than the osmotic pressure inside the red blood cells, the solution is hypertonic. The water inside the blood cells exits the cells in an attempt to equalize the osmotic pressure, causing the cells to shrink.
Isotonic Solution or IsotonicityWhen the osmotic pressure outside the red blood cells is the same as the pressure inside the cells, the solution is isotonic with respect to the cytoplasm. This is the usual condition of red blood cells in plasma. The cells are normal.
Hypotonic Solution or HypotonicityWhen the solution outside of the red blood cells has a lower osmotic pressure than the cytoplasm of the red blood cells, the solution is hypotonic with respect to the cells. The cells take in water in an attempt to equalize the osmotic pressure, causing them to swell and potentially burst.