In the nonobese subject, approximately 60% of total body mass consists of water, of which two-thirds is within cells. Of the one-third confined to the extracellular space, 70% is distributed in the interstitium, 20% in the vasculature, and 10% in the central nervous system, eyes, serous cavities, and intestinal lumen. Thus a 70 kg man carries 40 kg of water, of which 24 kg is contained within cells, 11 kg within the interstitium, 3 kg in plasma, and 2 kg in other compartments.
Interstitial fluid confers a degree of turgor that the practiced examiner recognizes as normal. Although modest expansion of interstitial fluid volume may not be detected, an excess of several liters causes visible and palpable swelling. The term edema refers to a discernible excess of interstitial fluid. Pitting edema gives way on palpation, leaving persistent impressions in the skin; brawny edema offers resistance and leaves no impressions.
Copyright © 1990, Butterworth Publishers, a division of Reed Publishing.