Fluid compartments

Fluid compartments in the mammalian body broadly comprise two compartments, each with several subdivisions: intracellular fluid, which makes up approximately 60-65% of body water, and extracellular fluid, which makes up the other 35-40% of body water. (For all practical purposes, the only solvent in the body is water)

Intracellular fluid
Intracellular fluid is found inside the bilayered plasma membrane, and is the matrix in which cellular organelles are suspended, and chemical reactions take place. The intracellular compartment contains on average about 28 liters of fluid, and under ordinary circumstances remains inosmotic equilibrium with the ECF.

Extravascular compartment
Outside the plasma membrane the cell is continually bathed in interstitial fluid ,which is the immediate microenvironment that allows for movement of ions, proteins and nutrients across the cell barrier. This fluid is not static, but is continally being refreshed and recollected by lymphatic channels. In the average male (70kg)human body, the interstitial space has approximately 11 liters of fluid.

Intravascular compartment
The main intravascular fluid in mammals is blood which is a complex fluid with elements of a suspension (blood cells), colloid(globulins) and solvent(glucose and ions).The average volume of plasma in the average (70kg) male is approximately 3liters.The volume of the intravascular lumen is regulated in part by hydrostatic pressure gradients,and by readsorbtion by the kidneys.