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Medical Definition of Extracellular fluid volume
1. The fraction of body wate rnot in cells; about 25% of body weight. It consists of plasma water (4.5% of body weight), water between cells (interstitial water-lymph, 11.5% of body weight), water in dense bone and connective tissue (7.5% of body weight) and water secretions.See transcellular water, about 1.5% of body weight.. (05 Mar 2000)