extracellular fluid (ECF) - Contents of ECF

The fluid which surrounds the cells of the body. In humans the adult volume is c.14 l/25 UK pt/30 US pt, and consists of blood plasma, the interstitial fluid of tissues, and transcellular fluids. Its principal components (apart from water) are sodium, chloride and bicarbonate ions, and proteins. The concept that the body's cells are protected from a continuously changing and often hostile external environment by their own internal environment, a fluid of constant volume and composition, was introduced by French physiologist, Claude Bernard (1813–78). Although the basic concept still holds, extracellular fluid is no longer considered to be constant, but to vary within very narrow limits.

In some animals, including mammals, the extracellular fluid can be divided into 2 major subcompartments, interstitial fluid and blood plasma.

Total extracellular fluid composes 1/3 of total body water volume, the other 2/3 being intracellular fluid.

Contents of ECF

Main Cations: Sodium (140 mM) Potassium (4 mM) Calcium (2 mM)

Main Anions: Chloride (110 mM) Hydrogen Carbonate (26 mM)

It is poorer in proteins compared to intracellular fluid