Medical Lecture Notes

A BLOG FOR all medical students contains a lot of knowledge in beautiful perfect notes.

Monday, 4 March 2019

Measurement of total body water

Measurement of total body water

  • Using the dilution method by injecting a substance which diffuses freely in all fluid compartment Substance used :
  1. Deuterium oxide (D2O)
  2. Tritiated water 3(H2O)
  3. antipyrine and amino-antipyrine

  • A sample of plasma obtained to measure concentration=Q/C

Measurement of ECF :

  • Two types of substance use:
  1. Saccharides: eg inulin, sucrose, mannitol
  2. diffusable ions: eg chloride, bromide, Na+

Measurement of ICF :

  • No substances can diffuse only in ICF
  • Total body water – ECF

        Measurement of plasma :

  • Substance used:

  1. Evans blue; which bind to plasma protein
  2. Albumins labeled with radioactive iodine

Measurement of blood :

  • Dilution method using red blood cells labeled with radioactive chromium 51(Cr) By use of plasma volume 

Interstitial fluid :

  • Interstitial fluid = ECF – plasma volume

Factors affecting body fluids :

  1. Osmosis: Movement of solvent molecules into a region in which there is a higher concentration of solute to which the membrane is semi-permeable.   
  2. Diffusion: It is an expansion of a gas or substance through a cell membrane, due to continuous random movement of its molecules. Water will follow this molecule into or out of the cell 
  3. Gibbs Donnan effect: the presence of nondiffusible anions like proteins and organic phosphate within the cell will affect the distribution of diffusible Anions –ve charged and Cations +ve charged.  [KX] [Cl-X] = [K+Y ] [Cl-Y ]

No comments:

Post a Comment