Renal Doubts

[AZ7]

Can anyone explain why Plasma volume can be measured using Albumin and Extracellular Fluid by Inulin or Mannitol ? FA 2016 Page 533
Also Page 534 says " Incremental reductions in GFR define the stages of chronic kidney disease " . What does this mean and how can we be tested on this?

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[jqueb29]

Can anyone explain why Plasma volume can be measured using Albumin and Extracellular Fluid by Inulin or Mannitol ? FA 2016 Page 533
Also Page 534 says " Incremental reductions in GFR define the stages of chronic kidney disease " . What does this mean and how can we be tested on this?

1. ECF volume is determined by 2 components, plasma volume and interstitial fluid volume. To determine plasma volume, we must use a marker that is too big to cross the capillary walls, such as albumin. Inulin and mannitol are able to cross through the capillary wall (i.e., they are able to enter the interstitium), but they are not able to enter cells, so these markers are confined to the plasma and interstitial fluid, and ECF volume = plasma volume + interstitial volume.

2. GFR is measured in units of mL/min, and each individual nephron contributes to the amount of mL that can be filtered every minute. So that means, if the number of nephrons decreases (as in chronic kidney disease), the GFR will also decrease. As more and more nephrons are lost (i.e., as chronic kidney disease progresses), the GFR decreases more and more.