aahy1978
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hi guys,
trying to go over some renal phys... and i can't understand the concept of Renal Plasma Flow... According to the BRS Physiology (3rd Edition)... in table 5-3.... increased plasma (protien) would decrease the GFR but it has no effect on RPF...
what is RPF... if the plasma is increased, shouldn't there be more flowing thru the kidneys....
also, what situation would increase RPF
anyway, any help would be awesome...
thanx
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| mdwannabe
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GFR is dependent upon the 4 forces coacting/counteracting eachother. The oncotic pressure in vessel is counteracted by hydrostatic pressure with Hydrostatics winning it by a little bit. In the Bowman's space oncotic pressure should be almost 0 and hydrostatic pressure not very high because of good elimination of urine to the toilet or the alley like I do :-)
So, with such discrepancy the filtration is preferred to Bowman's space. However, once you disrupt the ballance of forces by increasing Pull pressure in vessels (Albumin concentr incresed) the GFR will go down, because less filtrate will be able to escape the vessel.
Now if you look at flow accross the glomerulus, we would talk about plasma flow, rather that blood, because that is where the ultrafiltrate is comming from the main determinant of it is the contraction and dilation of Eff and Aff arterioles, which affects the amount of plasma in the limited space of glomerulus at any given time. Which in turn affect GFR by changing hydrostatic pressures. ( Example, Dilate Eff and leave Aff as is..the flow increases GFR goes up slightly, Constr Eff and leave Aff as is, flow goes down, GFR goes down etc.)
So, since in ur case the only thing changed is oncotic pressure, that change will not affect the flow at all, so RPF stays the same, but GFR goes down, for all the abovementioned reasons.
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| aahy1978
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i think i get it now... thanx mdwannabe
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| mdwannabe
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any time! :-)
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| luckiest
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HI mdwannabe thanks for great explanation but..due to my renal knowledge flaws i get lost..
1.SO GFR depend primarily on oncotic,hydrostatic pressure right?
2.Then if increase oncotic , decrease hydorstastic
the whole blood was pool in glomerulus instead of push out.
3.RIght here where I get lost.
renal plasma flow is determine by eff,aff arteriloe
TO me it ssems like GFR mean the same thing as RPF(the volume of plasma push through glomerulus
/ time)
WOuld you plese tell me where I get lost? :oops:
arrognace and ignorance are fools
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| mdwannabe
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1. GFR is dependent among other things on the RPF...just think about it outloud...GFR is the rate at which the ultrafiltrate leaves the system. RPF is the amount of plasma arriving for clearance to the glomerulus. So if more plasma (where ultrafiltrate comes from) arrives (RPF up, that is dependent on Card Output, vaso status etc.) and nothing else changes, then GFR should go up. However, as above, GFR is also dependent on pressures, so the same regulatory mechanisms that affect RPF will affect GFR, but not vise versa.
2. If Blood pools in glomerulus, the GFR will go up, don't mean to confuse you, just recall physicis of fluids, the slower the flow in the system the more mural pressure the fluid exerts, hence the blood will press harder upon capilary wall, increasing amount of stuff filtered, hence incresed GFR.
3. Again RPF is the amount of plasma going b/w Eff and Aff arteriole in a given time, not the amount of plasma pushing through glomerulus, though it does pass the tuft, it is only a short stop on the longer road. That is how I prefer to think about it.
Hope this helps.
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| sr
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umm constricting the efferent and dilating the aff increases gfr, not decrease. correct? above you wrote the opposite. likewise, constricting the aff and dilating eff decreases the gfr.
thats what i was taught. yes or no?
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| mdwannabe
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that is correct. I think I wrote the same thing. Unless I am reading my own post wrong. Can you please highlight where did I write this? ... I think I see where I wrote this...the first post??? It should read Dialte Eff ...remain Aff the same. That will increase GFR. Is that what you disputing?
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| sr
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yes. im saying that dilate eff and reduce gfr. you are saying the opposite. ????
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| mdwannabe
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:!:
not at all...it is an atypo... I appologize... I should reread my posts more carefully before posting. Thank you for noticing.
To clear the atypo...
GFR will increase once the Aff (or the incoming arteriole) will dialte, and the Eff (or the outgoing arteriole) stays the same. That is just one specific example.
If you dilate the Aff...and leave Eff as is...you are increasing amount of plasma in glomerulus at any given time, thus increasing GFR.
Aff arteiole-->Glomerulus-->Eff ateriole
http://www.bartleby.com/107/illus1129.html
Thank you.[/url]
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| luckiest
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thamk you for clea that up
I 've seen the illustrated why does it label only eff. vein ?
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| mdwannabe
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Thats how Gray drew it, and that is how it is. The vein does not start untill after second cap system. But he did not call it arterioles, he called it vessells. So efferent v. is efferent vessell.
Thats just my guess. :-)
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