BODY FLUIDS

The body's water is effectively compartmentalized into several major divisions.

INTRACELLULAR FLUID

Intracellular Fluid (ICF) comprises 2/3 of the body's water.

i.)If your body has 60% water, ICF is about 40% of your weight.

ii.)The ICF is primarily a solution of potassium and organic anions, proteins etc.

iii.)The cell membranes and cellular metabolism control the constituents of this ICF.

iv.)ICF is not homogeneous in your body. It represents a conglomeration of fluids from all the different cells.

EXTRACELLULAR FLUID

Extracellular Fluid (ECF) is the remaining 1/3 of your body's water.

i.)ECF is about 20% of your weight.

ii.)The ECF is primarily a NaCl and NaHCO3 solution.



The ECF is further subdivided into three subcompartments:

i.)Interstitial Fluid (ISF) surrounds the cells, but does not circulate. It comprises about 3/4 of the ECF.

ii.)Plasma circulates as the extracellular component of blood. It makes up about 1/4 of the ECF.

iii.)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.


(PERCENTAGE OF BODY COMPOSITIONS)
(PV-PLASMA VOLUME, ISF-INTERSTITIAL FLUID, PV+ISF=ECF, ECF-EXTRACELLULAR FLUID, ICF-INTRACELLULAR FLUID, ECF+ICF=TOTAL BODY WATER)

NOTES :

i.)All the body's fluid compartments are in osmotic equilibrium (except for transient changes).

ii.)The ions and small solutes that constitute the ECF are in equilibrium with similar concentrations in each subcompartment.

iii.)The ECF volume is proportional to the total Na content.



PRINCIPAL ELECTROLYTES OF BODY FLUIDS