QS Study

Body fluid distribution

The total amount of water present in the both is called body water. Body fluids are liquids originating from inside the bodies of living humans. They include fluids that are excreted or secreted from the body. The total body fluid is mainly distributed between two compartments: The extracellular fluid and the intracellular fluid. The Extracellular fluid (ECF) in turn is divided into the interstitial fluid and the blood plasma. There is another compartment of fluid that is transcellular fluid. This compartment includes fluid in synovial, peritoneal, pericardial and intraocular space as well as cerebrospinal fluid. All the transcellular fluid constitute about 1 to 2 liter. Water makes up 50 to 70 percent of the weight of the adult human body and varies inversely as the fat content.

Fig: Body fluid distribution

Distribution of water within the body

Intracellular Fluid (ICF): The amount of water that’s inside our cells accounts for 2/3rds of our TBW.

Extracellular Fluid (ECF): The amount of water that surrounds our cells accounts for 1/3 of our TBW. ECF is also known as interstitial fluid because it’s the fluid in between the cells.

Mnemonic to help you remember which is 1/3rd and 2/3rd:  ECF and ICF.  E comes before I in the alphabet, so E is 1/3rd and I is 2/3rd.

ICF = 2/3 X TBW. For example, 2/3 x 41L = 27L

ECF = 1/3 X TBW. For example, 1/3 x 41L = 14L

Daily water intake-output chart –

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