Darth _Vader Sidious_Maul
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A physiology question for those of you that are taking the USMLE step1…
Please I have to say this is the best forum because there are so many people that come through here every day that’s great if you want to get your returns and what not…
Well I have a question I hope that some of you can help me with I cant think straight on this I really need for you to talk to me like I am a 6 years old…lol
Ok here it the question:
What is it mean when you say that: 1. If Cx< GFR, then there is net tubular reabsorption of x
2. If Cx> GFR, then there is net tubular secretion of x
3. If Cx = GFR, then there is no net secretion or reabsorption?
Please I really don’t understand this could you please explain it to me like I am a 6 years old please
Thx for your time…
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| md2b
Forum Newbie
Topics: 1
Posts: 16
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Let me see if I can do this properly.....
1) If a certain amount of a substance (x) can be filtered by the glomeruli in a given period of time, then we will call that amount GFR. Cx indicates the Concentration of substance (x) in post-tubular filtrate.
However, if in the end the concentration in post-tubular filtrate (let's just call it urine for simplicity, though it is not until it reaches the bladder) of that substance (x) is less than the GFR would indicate it SHOULD be.....it was reabsorbed.
So you could say, if Cx < GFR, then it was reabsorbed somewhere...ie; tubular reabsorption.
2) Following that same line of thought, if someone were to measure the amount of substance x in urine, and it was GREATER than the filtration rate produced by the glomeruli, then it must also have been secreted by tubular cells. Hence tubular secretion.
So, Cx > GFR, because what you really have is GFR of that substance PLUS secretion, which means an amount greater than just GFR by itself.
3) Finally, you may have a situation where a substance is filtered......may even be secreted (or may not), but the reabsorption rate MATCHES the secretion rate (if it was indeed secreted or absorbed at all).
In this case, secretion and reabsorption rates cancel each other, and all you have left was your original GFR. If it was never secreted or reabsorbed you get the same end result.....only GFR.
So you can say that Cx = GFR, because the concentration of x will be exactly what your GFR can produce.
Hope this helps,
Aron
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| Darth _Vader Sidious_Maul
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thx
so much for you time...
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| md2b
Forum Newbie
Topics: 1
Posts: 16
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welcome....hope it helped.
Aron
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