Biochemistry, Hypertonicity

Excerpt

Tonicity

Tonicity is the capability of a solution to modify the volume of cells by altering their water content. The movement of water into a cell can lead to hypotonicity or hypertonicity when water moves out of the cell. The water movement then causes the cell to swell or shrink in size through osmotic pressure differences between the intracellular compartment (IC) and the solution tested. Solutions are isotonic when the volume of cells suspended in them does not change by osmotic fluid transfers.

Osmosis

Osmosis refers to the net movement of water, across a selectively permeable membrane, towards the location of higher osmotic concentration.

Osmolarity

Osmolarity is the term used for describing the concentration of solutes within a fluid. The terms isotonic, hypertonic, and hypotonic compare the osmolarity of a cell to the osmolarity of the extracellular fluid around it. Hyperosmolarity doesn't always mean hypertonicity because this depends on the solutes. Solutes such as Na+ and glucose, for example, need transporters. They contribute to serum tonicity and are termed effective osmoles (contributing to osmolarity). Meanwhile, urea and ethanol easily pass through cell membranes, contributing to serum osmolality but not tonicity.