Inulin is used for the measurement of-

Ans. is 'a' i.e., ECF * The volume of the various body compartments can be measured by injecting into them an indicator substance (marker or dye) and estimating its volume of distribution.* Measurement of body fluid volumes is done by 'Dilution method' i.e., by knowing the diluted concentration of dye in the fluid. Suppose 5 gm of dye is added to a beaker containing unknown volume of water. After equilibrium, if the marker concentration in water is lg/100 ml, the waterin the beaker can calculated as follows : Volume of water =Total amount of marker--------------------Concentration of marker in water=5g-----1g/100 ml= 500 ml Volume of fluid =Total amount of marker injected------------------------------Concentration of marker in the fluid, to be measured* Most of the fluid are calculated directly by dilution method, except for intracellular fluid (ICF) and interstitial fluid. Both these are calculated indirectly by calculating other body fluids.ICF = Total body water volume - ECF volumeInterstitial fluid = ECF volume - Plasma volume* Dyes used for various fluid volume measurement are : -Fluid volumeDye/indicator usedTotal body water (TBW) volumeDeuterium oxide: D2O (most commonly used), tritium oxide (3H2O), Aminopyrine, AntipyrineExtracellular fluid (ECF) volumeInulin (most accurate), Sucrose, Mannitol, Sodium thiosulfate, Na22, I125- iothalamatePlasma volume (PV)Evans Blue (T-1824), Serum albumin labeled with radioactive iodine(I125)Blood cell volumeCr51 labeled RBC