Tonicity

This article explains tonicity ; for an explanation of the terms hypertonicity and hypotonicity previously used in medicine, see arterial hypertension and arterial hypotension .

Tonicity ( Greek τόνος tónos , tension, tension '), also referred to as "effective osmolarity ", is a qualitative measure of the difference in osmotic pressure between two solutions based on a cell type (with its respective semi-permeability ). In contrast to osmolarity, tonicity has no unit .

meaning

Schematic representation of red blood cells ( erythrocytes ) in a surrounding medium (shown in black) that is hyper-, iso- or hypotonic with respect to the cytoplasm inside the cell.

The term tonicity is often used in biological medicine and biochemistry to describe the behavior of cells (the cytoplasm is "solution I") that are surrounded by a liquid ("solution II") through their cell membrane ("semipermeable membrane"). are separated. Since the tonicity is described as the difference in osmotic pressure, it is only caused by dissolved substances which - if an equilibrium is established - can not cross the membrane . Dissolved substances that can move freely through the membrane have no effect on tonicity.

Typical systems in which the term tonicity plays a role and is used are e.g. B. blood cells in serum , prokaryotes in fermentation medium , eukaryotic animal, plant or fungal cells in a purely chemically composed buffer or a complex composed nutrient medium and artificial membrane vesicles ( liposomes ) - z. B. in reconstitution experiments - in physiological buffers.

Terms

The tonicity is named in different terms: hypertonic, isotonic and hypotonic.

Hypertonicity

The term hypertonic ( syn. Hypertonic ; Greek ὑπέρ , over 'and tónos , tension, tension') means in biochemistry and biology:

• A solution has a higher osmotic pressure than a comparison medium.
• A cell (more precisely: the cytoplasm , the medium inside a cell) has a higher osmotic pressure than the medium surrounding it (the fluid outside the cell).

Isotonicity

The term isotonic (syn. Isotonic ; from the Greek ἴσος ísos 'equal' and τόνος tónos 'tension, tension') means in biochemistry and biology:

• A solution has the same osmotic pressure as a comparison medium.
• A cell (more precisely: the cytoplasm, the medium inside a cell) has the same osmotic pressure as the medium surrounding it (the fluid outside the cell).

In medicine, isotonic means:

• A solution has the same osmotic pressure as human blood.

Hypotonicity

The term hypotonic (syn. Hypotonic ; Greek ὑπό hypo 'under' and τόνος tónos 'tension, tension') means in biochemistry and biology:

• A solution has a lower osmotic pressure than a comparison medium.
• A cell (more precisely: the cytoplasm, the medium within a cell) has a lower osmotic pressure than the medium surrounding it (the fluid outside the cell).

Other meanings in medicine

Hypertension, hypertonic, hypertonic

• Technical term for high blood pressure
• Technical term for the tension of the muscles, d. H. the muscle tone is unphysiologically increased .

Isotonic

• Technical term: The muscle shortens without any change in force ("tensioned").

Hypotension, hypotonic

• Technical term for low blood pressure
• Technical term for the tension of the muscles, d. H. the muscle tone is unphysiologically low.

Web links

Wiktionary: isotonic  - explanations of meanings, word origins, synonyms, translations

Wiktionary: tonic  - explanations of meanings, word origins, synonyms, translations

literature

• Dee U. Silverthorn: Physiologie , 4th updated edition, Pearson Studium, Munich et al. 2009, ISBN 978-3-8273-7333-5 , pp. 236-238 .

Individual evidence

1. ^ Hans Walter Striebel: The operative intensive care medicine. Safety in clinical practice. Schattauer, Stuttgart et al. 2008, ISBN 978-3-7945-2480-8 , p. 123 .
2. ↑ Gary Gill: Cytopreparation. Springer Science & Business Media, 2012, ISBN 978-1-461-44933-1 , p. 37.