The human body is about 60 percent water. About two-thirds of that water is found inside cells, but the other third is outside cells and is known as “interstitial” fluid. Although researchers already knew that there is fluid between individual cells, the idea of a larger, connected interstitium — in which there are fluid-filled spaces within tissues — had been described only vaguely in the literature, Theise said. The new study, he said, expands the concept of the interstitium by showing these structured, fluid-filled spaces within tissues, and is the first to define the interstitium as an organ in and of itself.

Meet Your ‘Interstitium,’ A Newfound Organ

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