Filtration Fraction in Renal Artery stenosis - USMLE Forums
USMLE Forums Logo
USMLE Forums         Your Reliable USMLE Online Community     Members     Posts
Home
USMLE Articles
USMLE News
USMLE Polls
USMLE Books
USMLE Apps
Go Back   USMLE Forums > USMLE Step 1 Forum

USMLE Step 1 Forum USMLE Step 1 Discussion Forum: Let's talk about anything related to USMLE Step 1 exam


Reply
 
Thread Tools Search this Thread Display Modes
  #1  
Old 08-24-2011
drnirajmavani's Avatar
USMLE Forums Veteran
 
Steps History: Step 1 Only
Posts: 268
Threads: 14
Thanked 103 Times in 69 Posts
Reputation: 113
Kidney Filtration Fraction in Renal Artery stenosis

Like FF in constriction of afferent arteriole does not change (FF=GFR/RPF), does the FF in renal artery stenosis also does not change or is it increased ??
Reply With Quote Quick reply to this message



  #2  
Old 08-25-2011
USMLE Forums Master
 
Steps History: 1+CK+CS+3
Posts: 1,175
Threads: 38
Thanked 852 Times in 478 Posts
Reputation: 862
Default

Quote:
Originally Posted by drnirajmavani View Post
Like FF in constriction of afferent arteriole does not change (FF=GFR/RPF), does the FF in renal artery stenosis also does not change or is it increased ??
The decreased perfusion pressure (caused by the stenosis) leads to decreased blood flow to the kidney and a decrease in the GFR. If the stenosis is longstanding and severe the GFR in the affected kidneys never increases again which results in RF.

So in case of FF = GFR / RPF it would remain same since both GFR and RBF Decreased.
__________________
PGY-3
To view links or images in signatures your post count must be 10 or greater. You currently have 0 posts.

Last edited by patelMD; 08-25-2011 at 01:47 PM.
Reply With Quote Quick reply to this message
The above post was thanked by:
drnirajmavani (08-25-2011)
  #3  
Old 08-25-2011
drnirajmavani's Avatar
USMLE Forums Veteran
 
Steps History: Step 1 Only
Posts: 268
Threads: 14
Thanked 103 Times in 69 Posts
Reputation: 113
Default

Quote:
Originally Posted by patelMD View Post
The decreased perfusion pressure (caused by the stenosis) leads to decreased blood flow to the kidney and a decrease in the GFR. If the stenosis is longstanding and severe the GFR in the affected kidneys never increases again which results in RF.

So in case of FF = GFR / RPF it would remain same since both GFR and RBF Decreased.
i got a que wrong on UWSA2 by using this same logic.... the que was abt reducing the diameter of renal art by 75% i.e. stenosis ---> resistance increase by 256 times ----> this decreases the RBF..this should also decrease the GFR and FF should remain constant ... but i got this wrong nd UWSA explanation said the FF INCREASES>... i dnt kno if i m missing out some concept in dis..
Reply With Quote Quick reply to this message
 
  #4  
Old 08-25-2011
USMLE Forums Guru
 
Steps History: Not yet
Posts: 324
Threads: 70
Thanked 238 Times in 144 Posts
Reputation: 248
Default

Quote:
Originally Posted by drnirajmavani View Post
i got a que wrong on UWSA2 by using this same logic.... the que was abt reducing the diameter of renal art by 75% i.e. stenosis ---> resistance increase by 256 times ----> this decreases the RBF..this should also decrease the GFR and FF should remain constant ... but i got this wrong nd UWSA explanation said the FF INCREASES>... i dnt kno if i m missing out some concept in dis..
The uworld explanation says that "renal afferent arteriolar dilation and constriction allow the glomerular capillary hydrostatic pressure and GFR to remain stable when arterial blood pressure is maintained between 80 and 180 mmHg.Below 80 mmHg ,GFR and capillary hydrostatic pressure will decrease.A decrease in renal artery radius of 75% may cause such a drastic decrease in renal arterial pressure"..
here i feel some contradiction in UW explanation..and the answer..or may be because I didnt understand it.

Also the increase in FF is due to decrease in RBF due to severe stenosis of renal artery..here UW does not explain the affect of GFR..

Last edited by struggle; 08-25-2011 at 07:19 PM. Reason: Added info
Reply With Quote Quick reply to this message
  #5  
Old 08-25-2011
drnirajmavani's Avatar
USMLE Forums Veteran
 
Steps History: Step 1 Only
Posts: 268
Threads: 14
Thanked 103 Times in 69 Posts
Reputation: 113
Default

Quote:
Originally Posted by struggle View Post
The uworld explanation says that "renal afferent arteriolar dilation and constriction allow the glomerular capillary hydrostatic pressure and GFR to remain stable when arterial blood pressure is maintained between 80 and 180 mmHg.Below 80 mmHg ,GFR and capillary hydrostatic pressure will decrease.A decrease in renal artery radius of 75% may cause such a drastic decrease in renal arterial pressure"..
here i feel some contradiction in UW explanation..and the answer..or may be because I didnt understand it.

Also the increase in FF is due to decrease in RBF due to severe stenosis of renal artery..here UW does not explain the affect of GFR..
so whats the bottomline...i hav my exam in a week , nd still strugglin for the answers...
Reply With Quote Quick reply to this message



Reply

Tags
Physiology-, Renal-

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the USMLE Forums forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Medical School
Choose "---" if you don't want to tell. AMG for US & Canadian medical schools. IMG for all other medical schools.
USMLE Steps History
What steps finished! Example: 1+CK+CS+3 = Passed Step 1, Step 2 CK, Step 2 CS, and Step 3.

Choose "---" if you don't want to tell.

Favorite USMLE Books
What USMLE books you really think are useful. Leave blank if you don't want to tell.
Location
Where you live. Leave blank if you don't want to tell.

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes


Similar Threads
Thread Thread Starter Forum Replies Last Post
Aortic Stenosis vs Idiopathic Calcified Aortic Stenosis Ace3 USMLE Step 2 CK Forum 12 07-30-2011 03:35 PM
Renin concentration in Renal Artery Stenosis! bebix USMLE Step 1 Forum 17 07-25-2011 03:13 PM
What's the role of ACE inhibitors in Renal Artery Stenosis? qurat21 USMLE Step 1 Forum 3 05-02-2011 10:13 PM
Calculate the filtration fraction aktorque USMLE Step 1 Forum 2 02-23-2011 10:14 PM
Left Ventricular Ejection Fraction of 25%! Seetal USMLE Step 1 Forum 8 04-18-2010 09:56 AM

RSS Feed
Find Us on Facebook
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2017 DragonByte Technologies Ltd.

USMLE® & other trade marks belong to their respective owners, read full disclaimer
USMLE Forums created under Creative Commons 3.0 License. (2009-2014)