- Total body water (TBW) is approximately 60% of body weight.
- The percentage of TBW is highest in newborns and adult males and lowest in adult females and in adults with a large amount of adipose tissue.
A. Distribution of water (Figure 5-1 and Table 5-1)
1. Intracellular fluid (ICF) -is 2/3 of TBW.
- The major anions of ICF are protein and organic phosphates [adenosine triphosphate (ATP), adenosine diphosphate (ADP), and adenosine monophosphate (AMP)].
2. Extracellular fluid (ECF)
- is composed of interstitial fluid and plasma.
- The major anions of ECF are CI" and HC03~.
a. Plasma is 1/4 of the ECF. Thus, it is 1/12 of TBW (1/4 x 1/3).
- The major plasma proteins are albumin and globulins.
b. Interstitial fluid is 3/4 of the ECF. Thus, it is 1/4 of TBW (3/4 x 1/3).
- The composition of interstitial fluid is the same as that of plasma except that it has little protein. Thus, interstitial fluid is an ultrafil-trate of plasma.
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