Page 1057 - Fundamentals of anatomy physiology

1044 Unit 5 Environmental Exchange
Figure 27–1 The Composition of the Human Body.

SOLID COMPONENTS (31.5 kg; 69.3 lb) WATER (38.5 kg; 84.7 lb)
15 20 Other

10 15 Plasma
5
Kg 10
Liters Interstitial
fluid

5

0 Lipids Minerals Carbohydrates Miscellaneous 0 Extracellular fluid
Proteins Intracellular fluid

a The body composition (by weight, averaged for both sexes) and major body fluid compartments of a 70-kg (154-lb) person. For technical
reasons, it is extremely difficult to determine the precise size of any of these compartments; estimates of their relative sizes vary widely.

WATER 60% WATER 50%

ICF ECF ICF ECF

Intracellular Interstitial Intracellular Interstitial
fluid 33% fluid 21.5% fluid 27% fluid 18%

Plasma 4.5% Other
body
Plasma 4.5% Other Solids 50% fluids
Solids 40% body (organic and inorganic materials) (≤1%)
(organic and inorganic materials) fluids
(≤1%)

SOLIDS 40% SOLIDS 50%

Adult males Adult females

27 b A comparison of the body compositions of adult males and females, ages 18–40 years.

In clinical situations, it is customary to estimate that two- Exchange among the subdivisions of the ECF occurs pri-
thirds of the total body water is in the ICF and one-third in the marily across the endothelial lining of capillaries. Fluid may
ECF. This ratio underestimates the real volume of the ECF, but also travel from the interstitial spaces to plasma through lym-
that underestimation is appropriate because portions of the phatic vessels that drain into the venous system. p. 810
ECF—including the water in bone, in many dense connective The kinds and quantities of dissolved electrolytes, proteins,
tissues, and in many of the minor ECF components—are rela- nutrients, and wastes in the ECF vary regionally. (For a chemi-
tively isolated. Exchange between these fluid volumes and the cal analysis of the composition of ECF compartments, see the
rest of the ECF takes place more slowly than does exchange be- Appendix.) Still, the variations among the compartments of the
tween plasma and other interstitial fluids. For this reason, they ECF seem minor compared with the major differences between
can be safely ignored in many cases. Clinical attention usually the ECF and the ICF.
focuses on the rapid fluid and solute movements that accom-
pany the administration of blood, plasma, or saline solutions The ECF and ICF are called fluid compartments, because
to counteract blood loss or dehydration. they commonly behave as separate sections. The presence of a
plasma membrane and active transport at the membrane surface