Intracellular Fluid (ICF)
- is 2/3 of TBW, 40% of body weight in man,
- water forms about 75 - 80%
- the major cations are K+ and Mg2+
- the major anions are protein and organic phosphates such as ATP, ADP and AMP;
- pH of ICF is 6.8 - 7.4 in dependence on the metabolic processes;
Extracellular Fluid (ECF)
- is 1/3 of TBW, 20% of body weight in man
- is comprised of interstitial fluid (16%) and plasma (4%). Interstitial fluid is the true body environment.
- water constitutes about 93% of the plasma compartment
- the major cation is Na+;
- the major anions are Cl- and HCO3-;
- the ions in ECF determine osmotic pressure and pH of the inner environment;
- osmolarity of the ECF is 290 mmol/kg of water;
- pH of ECF is 7.4
Transcellular water is a compartment of ECW. Divided from the others by capillary endothelia and by epithelia.
Plasma
- comprises 1/4 of the ECF
- it is therefore 1/12 of TBW
- the major plasma proteins are albumin and globulins
Interstitial fluid
- comprises 3/4 of the ECF;
- it is 1/4 of TBW
- the composition is the same as plasma except it has little protein;
- thus, interstitial fluid is an microfiltrate of plasma