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extracellular fluid n.
The interstitial fluid and the plasma, constituting about 20 percent of the weight of the body.
All fluid outside of cells, usually excluding transcellular fluid.
in biology, body fluid that is not contained in cells. It is found in blood, in lymph, in body cavities lined with serous (moisture-exuding) membrane, in the cavities and channels of the brain and spinal cord, and in muscular and other body tissues. It differs from intracellular fluid (fluid within the cells) in that it generally has a high concentration of sodium and low concentration of potassium, while intracellular fluid is high in potassium and low in sodium. The fluid is often secreted by cells to provide a constant environment for cellular operations