Northerncardinal

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I'm a bit confused about how uric acid (pKa = 5.4) gets precipitated in acidic environments...the distal tubules and collecting ducts? Is it the deprotonated (charged) form of uric acid that ppts or the protonated form??

Uric acid is soluble at physiological pH. how?
 

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Uric acid (obviously it is an acid)... So the DCT and the collecting tubule are the most acidic part of nephron... If you go back to gen chem, we can apply the common-ion effect concept to understand why uric acid precipitate (less soluble) in an acidic environment. i.e.. acids are less soluble in acidic environment.

Someone else can explain it in a more technical way IMO, but that's the way I understand it...
 
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OnePunchBiopsy

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I'm a bit confused about how uric acid (pKa = 5.4) gets precipitated in acidic environments...the distal tubules and collecting ducts? Is it the deprotonated (charged) form of uric acid that ppts or the protonated form??

Uric acid is soluble at physiological pH. how?
It does not precipitate as pure uric acid in the kidneys. It binds with calcium, forming calcium urate crystals.

It isn't a pH problem that causes calcium urate stones to form in the kidney, it is due to high plasma concentrations of urate in the body (like seen in gout), leading to high amounts in the renal pelvis.

Some patients also suffer from genetic hypercalcinuria, and release tons of ionized calcium into their urine, making it more likely to occur.
 

gettheleadout

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It does not precipitate as pure uric acid in the kidneys. It binds with calcium, forming calcium urate crystals.

It isn't a pH problem that causes calcium urate stones to form in the kidney, it is due to high plasma concentrations of urate in the body (like seen in gout), leading to high amounts in the renal pelvis.

Some patients also suffer from genetic hypercalcinuria, and release tons of ionized calcium into their urine, making it more likely to occur.
This isn't correct. Straight uric acid stones are a thing, and it is indeed a pH issue; uric acid stones are associated with persistently low urinary pH or low urine output, and part of the treatment is urinary alkalinization.

See: http://emedicine.medscape.com/article/983759-overview#a5