The state of being hypertonic, i.e. having a greater degree of tone or tension
In biology, tonicity pertains to two definitions. The first one is associated with the osmotic pressure exerted upon a membrane and the other is about tone or tension (in a muscle or an organ). Relevant terms include isotonicity, hypertonicity, and hypotonicity.
In general, hypertonicity is a condition characterized by the presence of a greater degree of tone or tension. In cellular level, hypertonicity is a property of a solution wherein the amount of solutes is higher than that of another solution. A solution is also hypotonic when a solution (or a fluid) has greater osmotic pressure than the other solution (or fluid). Solutions that have different tonicities will result in a net flow of water across the cell membrane. For example, blood serum that is hypertonic to a physiologic salt solution would result in the net movement of water molecules towards the area with less water concentration (or higher solute concentration) (i.e. blood serum).
In the tissue level, hypertonicity in a muscle would imply a greater degree of tone or tension as the length of the muscle changes. This is in contrast to a hypotonic muscle with a lesser degree of tone or tension. A muscle whose tension remains relatively constant is described to be isotonic.
Word origin: iso– + Greek tonos ("tension")
- hypertonic (adjective, of, pertaining to, or relating to, hypertonicity)