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Pronunciation: i'so-ton'ik


  1. Relating to isotonicity or isotonia.
  2. Having equal tension; denoting solutions possessing the same osmotic pressure; more specifically, limited to solutions in which cells neither swell nor shrink. Thus, a solution that is isosmotic with intracellular fluid will not be isotonic if it includes solute, such as urea, that freely permeates cell membranes.
  3. In physiology, denoting the condition when a contracting muscle shortens against a constant load, as when lifting a weight.

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© Copyright 2018 Wolters Kluwer. All Rights Reserved. Review date: Sep 19, 2016.