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Renal > 2 - Acid Base Physiology > Flashcards

2 - Acid Base Physiology Flashcards

1
Q

nl PCO2

A

40 mmHg

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2
Q

nl bicarb

A

24 mM

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3
Q

what amount of acid/base do the kidneys have to correct for every day just from body processes?

A

70 mmol of acid for a 70 kg person (about 1 mmol/kg)

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4
Q

henderson hasselbach eqn

A

[H+] = 24 x PCO2 / [bicarb]

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5
Q

3 main points / ways kidneys deal with acid base balance

A 
proximal acidification (bicarb reabs, no acid excretion)
titratable acids and ammonia (acid excreted)
distal acidification (acid excreted)
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6
Q

clinical way to tell if someone has proximal RTA

A

give them bicarb for like a week and they will stay low (~16-18) because they just can’t reabsorb any more

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7
Q

mechanism of proximal RTA

A

dec capacity for bicarb reabsorption (defect in Na-H exchange, CA enzyme, etc) > can’t maintain high enough bicarb level > acidosis

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8
Q

Fanconi syndrome

A

proximal tubular damage causing bicarbonaturia, glycosuria, aminoaciduria and phosphaturia

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9
Q

causes of RTA

A

idiopathic, myeloma, familial, heavy metal poisoning, CA inhibitors

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10
Q

how does titratable acid formation work?

A

water is converted to OH and H
OH joins CO2 to form NEW bicarb (reabsorbed)
H is secreted and joins HPO4 to form H2PO4

since the HPO4 is filtered, this is GFR DEPENDENT

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11
Q

how does ammonia excretion work?

A

NH4 and OH are formed in kidney cells from metabolism
OH joins CO2 to form NEW bicarb (reabsorbed)
NH4 is broken apart, both NH3 and H are secreted, and then they reform NH4 in the tubule

since this is generated by the kidney cells, it can respond to acid loads as long as the GFR > 40

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12
Q

what is the primary site of distal acidification?

A

type A intercalated cell

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13
Q

how does the distal acidification work?

A

2 ways:
secretion of H ions from breaking down H20 through proton pumps > forms NH4 in tubule

H-K exchange ATPase that secretes 1 H for every 1 K reabsorbed

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14
Q

mechanism for distal RTA

A

defect in hydrogen secretion in distal tubules

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15
Q

what effect does hypokalemia have on ammonia conc in urine?

A

inc secretion of NH3 b/c H moves into cells to maintain charge (intracellular acidosis) so more ammonium is secreted to compensate

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16
Q

effects of distal RTA

A 
tubule lumen is more negative
K excretion enhanced > hypokalemia
urine not as acidic
osteoporosis as bone is used as a buffer
hypercalciuria
kidney stones
17
Q

how does distal RTA cause kidney stones?

A

CaPO4 released from bones in response to acidemia
acidosis > retention of citrate in proximal tubule
high urine pH + inc CaPO4 > precipitation into stones

18
Q

causes of distal RTA

A 
idiopathic
familial
rheumatologic (RA, Sjogren's, SLE)
drugs (ampho B, ifosfamide, lithium)
renal transplant
cirrhosis
sickle cell
19
Q

type 4 RTA mechanism

A

low aldosterone is underlying cause (or principal cell Na channel defect that mimics low aldosterone)
> excess Na, inc charge in tubule lumen > less H pumped out into lumen
also low aldosterone causes hyperkalemia > inhibits proximal NH4 production and bicarb generation falls

20
Q

causes of type 4 RTA

A

diabetes
urinary obstruction
medications (bactrim, K sparing diuretics)
renal interstitial inflammation (allergic, SLE)

21
Q

which type of RTA has lowest bicarb levels generally?

A

distal

22
Q

which type of RTA will have hyperkalemia?

A

type 4

23
Q

which type of RTA will have high pH urine?

A

distal

24
Q

nephrolithiasis and nephrocalcinosis are assoc w/ which RTA?

A

distal

25
Q

which type of RTA is most likely to present along with aminoaciduria and/or glycosuria?

A

proximal

26
Q

urine “anion gap”

A

NH4 is indirectly measured in urine
if Cl > (Na+K) > inc NH4 in urine in response to acidosis
if “gap” is pos, NH4 is absent > kidney is not making ammonium > RTA

Renal (20 decks)

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