Composition of Body Fluids

Body fluid is mainly composed of water with dissolved electrolytes and non-electrolytes.

Electrolytes, such as inorganic salts, acids, and bases are compounds that can dissociate into ions.

Conversely, non-electrolytes are organic molecules like glucose, lipids, creatinine, and urea that are bound by covalent bonds and do not dissociate into ions.

The solute concentrations in the plasma, interstitial fluid, and intracellular fluid vary greatly.

Sodium and chloride are the principal ions in plasma and interstitial fluid, with smaller amounts of phosphate, bicarbonate, and other cations and anions.

Conversely, intracellular fluid has lower levels of sodium and chloride ions, with potassium as the primary cation and phosphate as the major anion. It also contains a significant amount of soluble proteins.

The plasma and interstitial fluid, which make up the extracellular fluid or ECF, form only a small proportion of the total body fluid but are clinically vital.

In hemorrhage or dehydration, blood or saline is administered primarily to maintain ECF, enabling rapid solute and fluid exchange between the blood plasma and the interstitial fluid.