Renal Sodium Excretion: conflicting sources

[IDoIt4Love]

*Edit: This question has been answered, for anyone else looking for an answer: dietary sodium is very different from filtered. We reabsorb almost all that we filter, but get rid of 95% of our sodium intake.*

BRS physiology and FA (2012) say that almost all filtered sodium is reabsorbed in the kidneys. There was a question in the Kaplan q-bank about a woman who consumes a boat load of sodium and asks for an estimate of her sodium excretion rate, if she hasn't been experiencing any weight gain. In the explanation to the question, it states that 95% of dietary sodium is excreted.

But FA and BRS both say that we reabsorb almost all filtered sodium....so I'm really confused...which is it?

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[COdoubleMO2theN]

BRS physiology and FA (2012) say that almost all filtered sodium is reabsorbed in the kidneys. There was a question in the Kaplan q-bank about a woman who consumes a boat load of sodium and asks for an estimate of her sodium excretion rate, if she hasn't been experiencing any weight gain. In the explanation to the question, it states that 95% of dietary sodium is excreted.

But FA and BRS both say that we reabsorb almost all filtered sodium....so I'm really confused...which is it?

What goes in = what goes out, therefore in a sodium load, our body will work to excrete the excess via diuresis (unless the patient is in renal failure or something). It's how our body maintains homeostasis.

 

[loveoforganic]

There's a big difference between dietary and filtered.

If you have an ECF volume of 18 L and that's filtered 10x a day with a sodium concentration of 135 mmol, that's 24.3 mol Na = 560 g Na filtered per day. Any reasonable intake should be wayyyy less than that. So I wouldn't disagree with the first statement nor the answer to the question

 

[JackShephard MD]

Yeah, as they said above, this is just tricky wording.

We excrete less than 1% of the sodium we filter. But we filter A TON... so 1% can easily be a lot.

Also, if we didn't excrete most of our dietary intake, we would have a positive sodium balance and eventually have extreme hypernatremia.

it states that 95% of dietary sodium is excreted.

But FA and BRS both say that we reabsorb almost all filtered sodium....so I'm really confused...which is it?

Both are correct.

 

[IDoIt4Love]

Ohhhh...yeah ok, dietary and filtered are quite different. Thanks for the clarification, everyone.