The Body Fluid Compartments: Extracellular(1/3) and Intracellular Fluids(2/3); Edema

The total body fluid is distributed mainly between two compartments: the extracellular fluid and the intracellular fluid.

The extracellular fluid is divided into the interstitial fluid(ISF), Intravascular(IVF)(blood plasma) & Transcellular fluid(TCF).

Transcellular fluid: Transcellular fluid is the fluid found in body cavities. This compartment includes fluid in the synovial, peritoneal, pericardial, bile,fluids of the digestive tract and intraocular spaces, as well as the cerebrospinal fluid; it is usually considered to be a specialized type of extracellular fluid, although in some cases its composition may differ markedly from that of the plasma or interstitial fluid.

Fat tissue is exceptional in its low water content (10%or less); thus, the total water content of a fat animal will be lower than that of a lean animal. In very lean cattle, about 70% of body weight is water, while in very fat animals  BW may account for only 40%. The average animal (neither fat nor lean) probably has water equivalent to 60% of its body weight.

Total body water (TBW; 60%): Intracellular fluid (ICF; 40%)+  Extracellular fluid (ECF; 20%

Extracellular fluid (ECF; 20%): Extracellular fluid (ECF; 20%)+Intravascular fluid (IVF = PV; 5%)+Transcellular fluid (TCF; usually a low percentage but variable amount)

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