|
Measuring Volumes
| |
Fluid Compartments in the Body
The body's water is effectively compartmentalized into several major divisions.
 | Intracellular Fluid (ICF) comprises 2/3 of the body's water.
 | If your body has 60% water, ICF is about 40% of your weight. |
| The ICF is primarily a solution of potassium and organic anions, proteins etc. (Cellular
Soup!). |
| The cell membranes and cellular metabolism control the constituents of this ICF. |
| ICF is not homogeneous in your body. It represents a conglomeration of fluids from
all the different cells. |
|
| Extracellular Fluid (ECF) is the remaining 1/3 of your body's water.
| ECF is about 20% of your weight. |
| The ECF is primarily a NaCl and NaHCO3 solution. |
| The ECF is further subdivided into three subcompartments:
 | Interstitial Fluid (ISF) surrounds the cells, but does not circulate.
It comprises about 3/4 of the ECF. |
| Plasma circulates as the extracellular component of blood. It
makes up about 1/4 of the ECF. |
| Transcellular fluid is a set of fluids that are outside of the normal
compartments. These 1-2 liters of fluid make up the CSF, Digestive Juices, Mucus,
etc. |
|
|
| 40% x 70 kg = 28 L
water |
ISF, 10 L |
P l
a
s
m
a, 4L |
T r
a
n
s,
1
L |
The 60-40-20 Rule: 60 % of body
weight is water
40% of body weight is intracellular fluids
20% of body weight is extracellular fluid |
Intracellular
Water =40% |
Extracellular=20% |
Total Body Water = 60% of weight |
Special Notes:
| All the body's fluid compartments are in osmotic equilibrium (except for transient
changes). |
| The ions and small solutes that constitute the ECF are in equilibrium with similar
concentrations in each subcompartment. |
| The ECF volume is proportional to the total Na content. |
|
