Extracellular fluid

Editor In-Chief: Henry A. Hoff

Extracellular fluid (ECF) usually denotes all body fluid outside of cells. The remainder is called intracellular fluid.

In some animals, including mammals, the extracellular fluid can be divided into two major subcompartments, interstitial fluid (ISF) and blood plasma. The extracellular fluid also includes the transcellular fluid (TCF) which makes up only about 2.5 percent of the ECF.

In humans, the normal glucose concentration of extracellular fluid that is regulated by homeostasis is approximately 5 mM.

The pH of extracellular fluid is tightly regulated by buffers around 7.4.

The volume of ECF is typically 15L (of which 12L is interstitial fluid and 3L as plasma)

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