ABSTRACT
Of the weight of an average child, 60% is composed of water, which is distributed between the intracellular and extracellular uid compartments. As a neonate, 70% of our weight is water, and the fraction of our body weight that is water decreases as we age. Adipose tissue has only 10% water content compared to most organs, which contain 70% to 80% water, and thus excess fat reduces the percentage of body weight that is water. e concept of body composition and maintenance of uid and electrolyte homeostasis is easily appreciated if we separate these compartments as is shown by the beaker lled with uid in Figure 11.1. e intracellular compartment comprises 60% of our total body water, with the extracellular compartment making up approximately 40%. e extracellular uid compartment is predominantly interstitial uid that bathes cells. A small component of extravascular uid is in the cerebrospinal uid, peritoneal
and pleural uid, intraorbital uid, lymph, and uid in joint spaces. e intravascular compartment is only one fourth of the extracellular uid volume. us, only approximately 7% to 10% of our total body water is intravascular. Maintenance of the volume and composition of the intravascular uid space is critical for survival.
