Water distribution in the bodyWater accounts for approximately 60% of the total body mass in a normal adult, making it the most abundant constituent of the human body. In terms of volume, the total body water in a man of average weight (79kg) is roughly 40L. Water provides the medium for the solubilization and passage if a multitude of nutrients, both organic and inorganic, from the blood to the cells and the return of metabolic products to the blood. It also serves as the medium in which the vast number of intracellular metabolic reactions takes place.
Total body water can theoretically be compartmentalized into two major reservoirs, the intracellular compartment, which includes all water enclosed within cell membranes. Of the 40L of total body water, the intracellular and extracellular compartments account for about 25L and 15L respectively. The anatomic extracellular water is functionally subdivided into plasma, which is cell free, intravascular water compartment, and the interstitial fluid (ISF), which directly bathes the extravascular cells provides the medium for the passages of nutrients and metabolic products reciprocally form the blood to those cells. The fraction of total body weight that is water and the percentage of total body water that is extracellular or intracellular do not remain constant during growth. When express as percentage of body weight, total body water decreases during gestation and early childhood, reaching adult values by about three years of age. During this time the extracellular water (expressed as a percentage of body weight) decreases while the intracellular water increases.
Water distribution in the body
