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Flashcards in 2 - Acid Base Physiology Deck (26):
1

nl PCO2

40 mmHg

2

nl bicarb

24 mM

3

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

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

4

henderson hasselbach eqn

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

5

3 main points / ways kidneys deal with acid base balance

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

6

clinical way to tell if someone has proximal RTA

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

7

mechanism of proximal RTA

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

8

Fanconi syndrome

proximal tubular damage causing bicarbonaturia, glycosuria, aminoaciduria and phosphaturia

9

causes of RTA

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

10

how does titratable acid formation work?

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

11

how does ammonia excretion work?

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

12

what is the primary site of distal acidification?

type A intercalated cell

13

how does the distal acidification work?

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

14

mechanism for distal RTA

defect in hydrogen secretion in distal tubules

15

what effect does hypokalemia have on ammonia conc in urine?

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

16

effects of distal RTA

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

how does distal RTA cause kidney stones?

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

18

causes of distal RTA

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

19

type 4 RTA mechanism

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

causes of type 4 RTA

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

21

which type of RTA has lowest bicarb levels generally?

distal

22

which type of RTA will have hyperkalemia?

type 4

23

which type of RTA will have high pH urine?

distal

24

nephrolithiasis and nephrocalcinosis are assoc w/ which RTA?

distal

25

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

proximal

26

urine "anion gap"

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