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3B week 1 - abnormal urine > acid base balance > Flashcards

acid base balance Flashcards

1
Q

what is the pH range for life to operate

A

6.8-7.8 (apart from exceptional circumstances eg. stomach)

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2
Q

what is the optimal blood pH range

A

7.35-7.45

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3
Q

Ka equation

A

[H+][A-]/[HA]

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4
Q

what is pKa

A

a number that describes the acidity of a particular molecule -> calculated by -log(Ka)

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5
Q

what is a buffered solution

A

a solution in which the addition of an acid or base does not affect the pH of the solution

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6
Q

what are the main physiological buffers (4)

A
  1. bicarbonate (HCO3-) -> this is the main buffer
  2. phosphate (H2PO4 r=or HPO42-)
  3. plasma proteins
  4. haemoglobin
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7
Q

what is a volatile acid

A

an acid that can be excreted by the lungs i.e. CO2

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8
Q

what is the biocarbonate/CO2 chemical equaiton

A

CO2 + H2O <–(carbonic anhydrase)–> H2CO3 <–> H+ + HCO3-

the latter step occurs via rapid ionisation

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9
Q

what happens to the deconjugated form of H2CO3

A

H+ excreted by kidneys; HCO3- reabsorbed by kidneys

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10
Q

what are the 3 lines of defence against pH reduction

A
  1. bicarbonate
  2. replenishment of bicarb by kidneys
  3. removal of CO2
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11
Q

what is the net endogenous acid production

A

The nonvolatile acid load -determined by the balance of acid and alkali precursors in the diet

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12
Q

how many days could a person survive without the production of new bicarb

A

5 days

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13
Q

what is renal net acid excretion

A

the net amount of acid excreted in the urine per unit time - Its value depends on urine flow rate, urine acid concentration, and the concentration of bicarbonate in the urine

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14
Q

what is acidemia

A

an arterial pH below the normal range (<7.35)

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15
Q

what is alkalemia

A

an arterial pH above the normal range(>7.45)

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16
Q

what is acidosis

A

a process that tends to lower the extracellular fluid pH

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17
Q

what is alkalosis

A

a process that tends to raise the extracellular fluid pH

18
Q

where is acid produced from in the body

A

tissue metabolism and diet

19
Q

where is bicarbonate filtered/resorbed

A

filtered at the glomerulus, resorbed at the tubules
(and <0.1% excreted in the urine)

20
Q

what is required to neutralise net endogenous acid production

A

reclamation of filtered bicarbonate and generation of new bicarb

21
Q

where does the majority of the bicarb resorption occur

A

in the proximal convoluted tubules -> this also means that this is where the most H+ is secreted as for each HCO3- reabsorbed, 2H+ are released

22
Q

bicarb resorption in the early tubular segments MOA (6)

A
  1. Na+/K+ ATPase results in build up of Na+ gradient extraceullularly in the renal peritubular fluid (3Na+ out, 2K+ in)
  2. this allows Na+ to move into the cell from the tubular lumen down its gradient (via Na+/H+ exchanger i.e. H+ out)
  3. HCO3- in the lumen bonds with H+ ion forming H2CO3
  4. this is then split into CO2 + H2O
  5. CO2 enters the cell where it is turned back into H2CO3 and then broken into HCO3-
  6. HCO3- excreted alongside Na+ via co transporter into the renal interstitial fluid (H+ then leaves cell via mech in step 2)

tubular lumen = filtrate from the glomerulus, interstitial fluid = blood

23
Q

what transporter is responsible for moving HCO3- into the renal interstitial fluid in the distal tubular segments

A

Cl-/HCO3- exchangers (down their concentration gradients)

24
Q

how is new bicarb generated in the kidneys

A

by product of ammoniagenesis

25
Q

why does bicarb have to be split into CO2 + H2O in order to enter the tubular cells

A

HCO- is too polar of a molecule so cannot pass through the lipophilic cell membrane, while H2O and CO2 are not as polar

26
Q

what is ammoniagenesis

A

the breakdown of amino acids (esp. glutamine) into ammonia -> triggered by acidosis

27
Q

why are buffers essential in urine

A

they allow H+ ions to be excreted without the pH of urine dropping below 4.0

28
Q

what is the normal urine pH range

A

4.5 - 8.0

29
Q

how does ammonia buffer the urine MOA

A
  1. ammonia is lipid soluble so it diffuses freely into the tubule, where it combines with a hydrogen ion to form an ammonium NH4+ ion
  2. Ammonium NH4+ combines with chloride Cl- in the urine -> Because ammonium chloride is only weakly acidic, the urine pH doesn’t drop much even though it now contains a lot of hydrogen H+ ions
30
Q

what is the secondary buffer system in the urine

A

phosphate

31
Q

how does phosphate act as a buffer

A
  1. acidosis stimulates the excretion of urinary phosphate
  2. HPO4^2- + H+ -> H2PO4-, binding happens in the tubular lumen with H+ excreted via the Na+/H+ exchanger
  3. H2PO4 is then excreted in the urine
32
Q

why is the byproduct of ammonia generation in ammoniagenesis

A

HCO3- -> this then enters the renal intersstitial lfuid

33
Q

what would happen to blood/urinary bicarb conc if a carbonic anhydrase inhibiting drug was adminstered

A

bicarb cant be reabsorbed as carbonic anhydrase is required for HCO3- to enter the cell and for H2CO3 to be deconjugated =>
urinary bicarb - increased
blood bicarb - decreased

34
Q

2 drugs which inhibit carbonic anhydrase

A
  1. acetazolamide (carbonic anhydrase inhibitor, used in glaucoma)
  2. topiramate (epilepsy, migraine)
35
Q

what is the urine anion gap

A

[(Na+ + K+) – (Cl−)]

used to roughly estimate whether urine ammonium is increased or decreased in the evaluation of hyperchloremic metabolic acidosis

36
Q

what is hyperchloremic metaboic acidosis

A

a pathological state that results from bicarbonate loss, rather than acid production or retention

37
Q

what does a negative urine anion gap indicate

A

more chloride than cations -> another cation is being excreted e.g. NH4

38
Q

what is the correct response to metabolic acidosis

A

increased renal ammonium excretion (-ve UAG)

39
Q

what does a negative urine anion gap indicate about the cause for metabolic acidosis

A

the tubular function is intact => extra renal cause for metabolic acidosis

40
Q

what does a positive urine anion gap indicate in metabolic acidosis

A

reduced renal ammonium excretion => reduced renal acid secretion -> renal tubular problem

41
Q

3 causes of respiratory alkalosis

A
  1. congestive cardiac failure
  2. raised ICP
  3. hyperventilation
42
Q

how is H+ secreted into the urine

A
  1. via Na+/H+ exchanger in the proximal convoluted tubule
  2. via H+ ATPase in the distal tubules

3B week 1 - abnormal urine (5 decks)

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