Step I Sodium Kidney Question

[SeminoleFan3]

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BRS Phys says that very little sodium is excreted in urine (<1% of the filtered load) because most of it is absorbed along the nephron. Then, how is it that we excrete 95% of the sodium we take in?

(Sorry if this is obvious, but I just can't seem to get it).

 

[NontradICUdoc]

You need to compare the ECF vs ICF. While we may excrete 95% of the Na we take in, this does not account for all of the Na in the body because most of it is in the ICF.

 

[512TA]

goljan has the following values up for normal functioning kidney:

FeNa<1
Urine Na<40

FeNa= (Urine Na times Plasma creatine)/(Urine creatine times plasma sodium) times 100

 

[Slide]

BRS Phys says that very little sodium is excreted in urine (<1% of the filtered load) because most of it is absorbed along the nephron. Then, how is it that we excrete 95% of the sodium we take in?

(Sorry if this is obvious, but I just can't seem to get it).

Don't forget that though very little sodium gets excreted per liter (considering normal sodium intake), a large amount of fluid flows through the kidney each day (I think 140-150 L a day). Even if only 1% of the sodium is excreted each time a liter goes through the kidneys, it adds up to be a lot.