Biomedical Engineering Reference
In-Depth Information
TABLE 7.1
Fluid Volumes in a 70 Kg Adult
Compartments
Volume in L
Total Fluid (60% of total body weight)
42
Intracellular
28
Extracellular
14
Interstitial
11
Blood
5
Plasma
3
Transcellular
1-2
Lymph
1
Intracellular Fluid
28 L
Input
Cell Membrane
Interstitial Fluid
11 L
Plasma
3 L
Capillary
Membrane
Capillary Membrane
Output
Lymph
1 L
Output
FIGURE 7.1
The compartment volumes of the body. A box depicts the volume. These volumes are tightly
controlled by the body through mechanisms that will be described in this chapter. The arrows indicate a flow from
one compartment into another (next to the arrows are the types of membranes the fluid must pass through). The
rate of flow through a membrane depends on the properties of the membrane. The input includes the fluid
ingested. Output is fluid lost from the kidneys, lungs, skin, and sweat, with a small amount lost in the feces.
Not shown is the transcellular fluid.
the lymph nodes. The white blood cells in the lymph nodes monitor the lymph and destroy
foreign substances to protect the body from disease. Figure 7.1 illustrates the relationships
among the compartments.
7.3 TRANSFER OF SUBSTANCES BETWEEN TWO
C
OMPARTMENTS SEPARATED BY A MEMBRAN
E
7.3.1 Diffusion and Membranes
Molecules and atoms randomly move due to thermal energy. They are never at rest even
though the medium in which they are present is still. The speed of the molecules depends
