EXTRACELLULAR FLUID

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-composed of intravascular compartment and interstitial compartment
-Na+ is the most important determinant for the extracellular osmotic pressure and volume
-changes in total body sodium content generally reflects the extracellular volume
Extracellular fluid provides a medium for:
-cellular nutrients and electrolyes
-cellular waste products

Interstitial fluid
Generally associated with:
-extracellular proteoglycans which forms a gel
-negative pressure  -5mmHg
-edema is generally associated with a positive interstitial fluid pressure

Intravascular fluid
-small electrolytes are able to pass freely from interstitium into the intravascular space
-identical electrolyte composition between the plasma intravascular space and interstitium
-plasma proteins (albumin) are the only osmotically active solute in the plasma that is not exchanged w.in the interstitial fluid
clinical example: tissue edema
-occurs with increased extracellular fluid volume
-interstitial pressure becomes positive
-additional increases in extracellular fluid expands the interstitial compartment
-resultant tissue edema