<P> Extracellular fluid (ECF) denotes all body fluid outside the cells . Total body water in humans makes up between 45 to 75% of total body weight . About two thirds of this is intracellular fluid within cells, and one third is the extracellular fluid . The main component of the extracellular fluid is the interstitial fluid that bathes cells . </P> <P> Extracellular fluid is the internal environment of all multicellular animals, and in those animals with a blood circulatory system a proportion of this fluid is blood plasma . Plasma and interstitial fluid are the two compartments that make up at least 97% of the ECF . Lymph makes up a small percentage of the interstitial fluid . The remaining small portion of the ECF includes the transcellular fluid (about 2.5%). The ECF can also be seen as having two components--plasma and lymph as a delivery system, and interstitial fluid for water and solute exchange with the cells . </P> <P> The extracellular fluid, in particular the interstitial fluid, constitutes the body's internal environment that bathes all of the cells in the body . The ECF composition is therefore crucial for their normal functions, and is maintained by a number of homeostatic mechanisms involving negative feedback . Homeostasis regulates, among others, the pH, sodium, potassium, and calcium concentrations in the ECF . The volume of body fluid, blood glucose, oxygen, and carbon dioxide levels are also tightly homeostatically maintained . </P> <P> The volume of extracellular fluid in a young adult male of 70 kg is 20% of body weight--about fourteen litres . Eleven litres is interstitial fluid and the remaining three litres is plasma . </P>

Where do you find interstitial fluid in the human body