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Old 06-05-2011
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Question ACIDOSIS and HYPERKALEMIA

hey guys with all types of acidosis we got HYPERKALEMIA....but with RTA type 1 and 2 we got HYPOKALEMIA...

Y?

i asked prof noto today he replied that IN TYPE 2 RTA there is problem with hco3 reabsorption so it GET LOST IN URINE with HCO3 Na and H2o--->hypovolumia--->inc aldosteron secretion to compensate hypovolemia--->increased k secretion---->hypokalemia..


in type 1 RTA late distal tubule cant secrete H+ into urine so alkaline urine is formed..BUT FOR HYPOKALEMIA I DONT KNOW HOE TO APPLY ALDOSTERONE HERE...
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Normally, we associate acidosis and hyperkalemia because when there is an excess of H+ in the blood, K+ leaves the cell in exchange for H+, thus hyperkalemia.

In RTA I and II, we have to look at the renal tubules.

In RTA I, H+ cannot be secreted properly. This is in part due to dysfunction of the H+/K+ exchanger in the distal tubule. Normally, H+ is secreted and K+ is absorbed. In RTA I, this is defective and thus K+ cannot be reabsorbed by this exchanger and is lost in urine --> Hypokalemia

In RTA II, there is defective HCO3- reabsorption. Since there is more HCO3-, more Na+ will follow because of opposite charge. This means that less Na+ is reabsorbed in the PCT and more is delivered to the DCT. In the distal tubule, the increased Na+ leads to increased exchange of Na+ and K+, with Na+ being reabsorbed and K+ being secreted. --> Hypokalemia (this mechanism is not very well established so if it doesn't make too much sense then I would just memorize the association)

Aldosterone increases H+ and K+ excretion in exchange for Na+ so increased aldosterone would lead to hypokalemia as well, but this is not really the mechanism in RTA I and II because the RAA system is not really involved in the pathogenesis

However, in RTA IV, aldosterone receptors are defective so the exchange of H+ and K+ for Na+ cannot take place, thus H+ and K+ are increased in the body --> Acidosis + Hyperkalemia

The reason for Hypokalemia in I and II is not that well understood but these are the mechanism I gathered from reading Uptodate. I researched this a couple months ago and this is what I came up with. Hope that makes sense.
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i dodnt know how to say thank you to you
i was actually totally messed up with this.....
i asked prof @ kaplan accademy he told me ALDESTERON thingy..

BTW i didnt find any h/k channel in tubule ...inkaplan physio

any way BOTTOM LINE is for usmle just know that in type 1 and 2 RTA we have HYPOKALEMIA..and for type 4 we have HYPERKALEMIA..

i think we should not go too deep ..m i right?
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Old 06-05-2011
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Quote:
Originally Posted by IKR123 View Post
i dodnt know how to say thank you to you
i was actually totally messed up with this.....
i asked prof @ kaplan accademy he told me ALDESTERON thingy..

BTW i didnt find any h/k channel in tubule ...inkaplan physio

any way BOTTOM LINE is for usmle just know that in type 1 and 2 RTA we have HYPOKALEMIA..and for type 4 we have HYPERKALEMIA..

i think we should not go too deep ..m i right?
you better find that channel
see the attached file (picture from netter physiology)
Attached Files
File Type: pdf Netter_s_Atlas_of_Human_Physiology.pdf (142.7 KB)
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Old 06-05-2011
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Quote:
Originally Posted by bebix View Post
you better find that channel
see the attached file (picture from netter physiology)
Attachment 1440
at

I cant find that channel
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Old 06-05-2011
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The H+/K+ Exchanger is located on Type A Intercalated cells of the collecting duct

http://en.wikipedia.org/wiki/Collect...rcalated_cells

I don't think it's included in review books because it is not that high yield but it is definitely present in the collecting duct and plays a role in H+ excretion and K+ absorption
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Old 06-05-2011
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Found a diagram that might help

ACIDOSIS and HYPERKALEMIA-type-cell.jpg
click image to enlarge
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Quote:
Originally Posted by pass7 View Post
at

I cant find that channel
"you better find that channel" was a joke
The pdf was trying to show the channels that we must know.

Thanks apx85 for the info.
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Old 06-08-2011
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dr noto is sooo good.. i attended class with him recently!
i wonder why kaplan doesnt use him or publicize him more..!!!!
hes worth every penny u pay
all ur concepts get crystal clear with him
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Old 06-08-2011
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hey mbbs u are attending him right now a days?
are u taking live @ net or live course?
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Old 06-09-2011
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Just also learned today that increased anions in the tubule lumen favors K+ secretion because of electronegative forces. Thus, in RTA II, the increased HCO3- in the lumen draws K+ out of the tubule cells (via simple diffusion) and increases K+ losses
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