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Urinary > Week 6 - Acid Base Balance > Flashcards

Week 6 - Acid Base Balance Flashcards

1
Q

What is alkalaemia/ acidaemia?

A
  • pH greater than 7.45 -> alkalaemia

- pH less than 7.35 -> acidaemia

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2
Q

What is the effect of alkalaemia on calcium ions? What is the consequence of this?

A
  • Lowers free calcium by causing the ions to come out of solution -> bound to albumin instead of H
  • Leads to increased neuronal excitability causing paresthesia and tetany
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3
Q

What effect does acidaemia have on K? What is the major consequence of this?

A

-Causes hyperkalaemia as H+ are taken into the cell in exchange for K+ in order to lower H+ conc

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4
Q

Why is a lower pH disruptive?

A

-Denatures proteins causing enzyme disturbances and affecting muscle contractility, glycolysis and hepatic function

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5
Q

Below what pH is life threatening?

A

-7.0

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6
Q

How is plasma pH determined?

A

-Ratio of [HCO3]/CO2

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7
Q

What is the henderson-hesselbach equation?

A
  • pH=pK+log([hco3]/(CO2 x0.23))

- pK is a constant = 6.1 at 37 degrees

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8
Q

What is the normal ratio of HCO3:CO2?

A

-20:1

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9
Q

What ultimately determines the pCO2?

A

-Respiration controlled by the chemoreceptors

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10
Q

What controls the concentration of HCO3?

A

-Kidneys

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11
Q

What is the effect of hypoventilation on partial pressures and acid base balance?

A

-Decreased pO2, increased pCO2 -> respiratory acidosis

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12
Q

What is the effect of hyperventilation on partial pressures and acid base balance?

A

-Increased pO2, decreased pCO2 -> respiratory alkalosis

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13
Q

What controls respiration?

A
  • Detectoion of pO2 and pCO2 by peripheral and central chemoreceptors respectively
  • Send information to respiratory centre in brain
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14
Q

How are respiratory changes in acid base balance corrected?

A

-Change in ventilation rate

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15
Q

How are respiratory changes in acid base balance compensated?

A

-Change in [HCO3]

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16
Q

What produces the main source of bicarb in the blood?

A

-RBCs

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17
Q

When is metabolic acidosis caused?

A

-When there is an increase in the production of acids produced by tissues which reacts with HCO3 and decreases pH

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18
Q

How are metabolic changes in acid base balance corrected?

A

-Increased HCO3 production or increased excretion

19
Q

How do the kidneys increase [HCO3]?

A
  • Recover all filtered HCO3

- Make new HCO3

20
Q

How do the kidneys produce HCO3?

A
  • Kidneys have high metabolic rate and produce lots of CO2
  • CO2 reacts with water to form HCO3 and H+
  • HCO3 enters plasma
  • H+ enters filtrate
21
Q

Describe the recovery of HCO3 in the kidneys

A
  • 80% resorption in PCT
  • NaKATPase sets up an Na gradient
  • NHE brings Na into the cell in exchange for H
  • H reacts with HCO3 to form CO2 and H2O
  • CO2 diffuses across membrane
  • CO2 reacts with H2O inside cell to produce HCO3 and H+
  • HCO3 is transported out of the basolateral membrane into plasma on a transporter with Na
22
Q

Which enzyme is present on apical tubular membrane that speeds up CO2 reactions?

A

-Carbonic Anhydrase

23
Q

Besides from CO2, how else do the kidneys make HCO3? give an example. What substance is excreted in urine because of this?

A
  • From Amino acids -> Glutamine to a-ketoglutarate

- Produces HCO3 and NH4+ (enters urine)

24
Q

What is different between HCO3 resorption from CO2 in PCT and HCO3 production in DCT?

A
  • In PCT Na gradient is sufficient to drive H+ out of cells into the tubule
  • In DCT, Na is mostly resorbed so the gradient is not sufficient. Therefore H+ is actively secreted into the lumen by H+ATPase
25
Q

How is H+ buffered in PCT and DCT?

A
  • PCT-> by secreted NH3

- DCT-> by secreted NH3 and by filtered HPO4

26
Q

In which cells of the DCT is HCO3 made?

A

-a-intercalated cells

27
Q

How are metabolic changes in acid base balance compensated?

A

-Changes in ventilation rate to increase/decrease pCO2

28
Q

How is metabolic acidosis compensated for?

A

-Increased breathing -> increased CO2 blown off -> decreased pCO2

29
Q

How is metabolic alkalosis compensated for? Why is this limited?

A
  • Decreased breathing -> decreased CO2 blown off -> increased pCO2
  • Limited by decreased in oxygen when decreasing breathing
30
Q

Commonly, when would metabolic alkalosis occur?

A

-After vomiting -> excreted all acid but HCO3 remains -> absorbed into blood stream -> alkalosis

31
Q

What is the minimum pH of urine?

A

-4.5

32
Q

How and why is acid excreted?

A
  • In the urine reacted with NH3 to produce NH4 or reacted with phosphate
  • If acid wasnt excreted it would react with HCO3 and acidosis would occur due to excessive HCO3
33
Q

What are the cellular responses to acidosis in the kidney?

A
  • Increased NHE activity -> more H+ secreted into lumen -> more HCO3 produced
  • Increased ammonium production in PCT to buffer H= for excretion
  • Increased H+ATPase in DCT
  • Increased capacity to export HCO3 from tubular cells into ECF
34
Q

What acids are often increased in metabolic acidosis?

A
  • Lactic acid

- Ketoacids

35
Q

What is the anion gap?

A
  • The difference between [Na]+[K] and [Cl] and [HCO3]

- Usually 10-15 mmol/l

36
Q

When does the anion gap increase?

A

-H+ from excess acid reacts with HCO3 and the HCO3 is replaced by the anion of that acid

37
Q

What is the benefit of the anion gap? Give an example of when it is increased

A
  • Shows wether there is acidosis due to a certain anion which has replaced HCO3
  • Seen in ketoacidosis
38
Q

From which organ does metabolic acidosis occur that does not effect the anion gap as HCO3 is replaced with Cl?

A

-Renal problems

39
Q

How is metabolic alkalosis corrected?

A

-Increased excretion of HCO3

40
Q

When is correction of metabolic alkalosis problematic?

A

-When there is also volume depletion because Na recovery is prioritised which increased NHE activity and thus increases HCO3 recovery

41
Q

What is the relationship between metabolic acidosis and hyperkalaemia?

A
  • metabolic acidosis -> increased H+ in ECF -> exchanged for K+ -> hyperkalaemia
  • Hyperkalaemia -> increased K+ in ECF -> exchanged for H+ -> metabolic acidosis
42
Q

What is the relatinship between metabolic alkalosis and hypokalaemia?

A
  • Metabolic alkalosis -> H+ moved into ECF in exchange for K+ -> hypokalaemia
  • Hypokalemia -> K+ moved into ECF in exchange for H+ -> metabolic alkalosis
43
Q

What is the range in which plasma pH has to be maintained?

A

-7.35-7.45

44
Q

Which acid is titratable in the urine?

A

-That which is bound to phosphate

Urinary (21 decks)

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