scorpio
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Dear Doctors,
I am new in this community but I am very much
excited to see how much supportive you guys are.I am reviewing
Physiology from Kaplan notes (2002 edition) and I do also need some
support from you guys.
Here is my concern:
How an increase intubular flow will increase Potassium secretion ?
(unless by another mechanism a potassium-sparing effect is produced)
[Kaplan Physiology page 353 explanation for Q-5]
Thanks for your time.
-Scorpio.
PS:My sincere thanks for the webmaster who created this excellent forum.
Edited by scorpio on 12/16/05 - 11:46 AM
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| scorpio
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2. How does renal tubular carbonic anhyhrase contribute to water reabsorption?
Thanks
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| msyamp
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High urinary flow rates stimulate K secretion in the cortical collecting duct (CCD). Both small-conductance secretory K and high-conductance Ca2+/stretch-activated maxi-K channels have been identified in the apical membrane of the mature CCD.
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd...
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| scorpio
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Thanks !
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| reet
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i have not checked question in notes.anyways..
Lemme' put it this way.... it might be a normal mechanism
increase in TUBULAR FLOW-- is controlled by 2 things ADH & ALDOSTERONE.
SO, Na and h2o reabsorption occurs..Now Na reabsortipn creating negative charge in tubular lumen which attracts K+ AND net secretion of K occurs.
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| reet
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oh!! msyamp.. good search....
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| msyamp
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renal tubular carbonic enhydrase will split h2co3 into h2o and co2.assissting co2 to get duffused across.
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| scorpio
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Dear msyamp and reet,
Let me summarise,
1. Increased tubulat flow will increase Na/H2O absorption in the distal collecting duct(ADH+Aldosteron effect) this will creat high -ve charge so more K will be secreted.
2.But I am still not sure how lumen CA contributes to the reabsorption of water and so Na+, HCO3- and K+.(Q-9 page 251)
(There might be good explanation in Pharma- MOA of Acetazolamide, but I'm not sure)
But you guys are awesome thanks .
-Scorpio
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| sturge_weber
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well for k secrn, there is one thing, as the body wants to reabsorb na, it does this by secreting the k, that is the na k atp ase....
well and for carbonic anyhydrase, it takes the luminal hco3- and also h+ and converts it to h2co3 , which then gets converted to h20 and co2, co2 diffuses, whereas this h20 is reabsorbed
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| reet
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coool!!!!!!!!!
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| msyamp
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Great Sturge!!!!
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| mildus
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About K
potassium is located in the cells (tubulocytes)
NaK ATPase is on the basolateral membrane of tubulocytes
sodium channels are on the luminal membrane
potassium channels are also on the luminal membrane
NaK ATPase maintains high intracellular potassium concentration, so there is more potassium in the cells than in the lumen of tubul and that is why potassium goes out from the cell into the lumen by way of simple diffusion through its channels on the luminal membrane
Potassium comes into the lumen as long as there is concentration gradient between the cell and the lumen
if tubular fluid stopped moving, potassium diffusion would also stop in the moment when its concentration became the same in the lumen as in the cell
so, if new tubular fluid arrives constantly and very fast, it will carry potassium away so the concentration gradient will persist and allow continuous potassium diffusion into the lumen
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| reet
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thanks mildus..i am real fan of ur explainations..keep posting ...
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