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Renal physiology > Acid-base balance II: Whole body acid-base balance > Flashcards

Acid-base balance II: Whole body acid-base balance Flashcards

1
Q

what is the first priority if normal acid-base balance is disrupted?

A

restore pH to 7.4 as soon as possible- compensation

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2
Q

what is compensation?

A

the restoration of pH irrespective of what happens to [HCO3-]p and PCO2

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3
Q

what is correction?

A

restoration of pH and [HCO3-]p and PCO2 to normal

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4
Q

what are the 2 classification of disturbances or respiratory origin?

A

-respiartory acidosis (plasma pH falls)
-Respiratory alkalosis
(plasma pH rises)

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5
Q

what are the 2 classification of disturbances or non-respiratory origin?

A

-Metabolic acidosis
(plasma pH falls)
-Metabolic alkalosis
(plasma pH rises)

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6
Q

what is immediate buffering of a pH change?

A

Immediate dilution of the acid or base in ECF
Blood buffers (i.e. Hb, HCO3-. Acidosis would reduce [HCO3-]p)
Buffers in the ECF (particularly HCO3-)

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7
Q

what happens once buffer stores are quickly depleted?

A

kidney has to rectify stores

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8
Q

what can measure pH and Pco2?

A

blood-gas analyser

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9
Q

what is pH proportional to?

A

[HCO3-]/ [CO2]

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10
Q

what diagram can we plott variables on?

A

Davenport diagram

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11
Q

what are the normal values in the davenport diagram?

A

plasma pH- 7.4

[HCO3-]p - 25mmol/l

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12
Q

what is respiratory acidosis?

A

retention of CO2 by the body e.g. chronic bronchitis

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13
Q

how do respiratory disorders generate acidosis?

A

Co2 retention drives equilibrium to the right

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14
Q

what happens during respiratory acidosis?

A

-Both [H+]p and [HCO3-]p rise
-The increased [H+]p results in acidosis
(remember that pH is only a measure of free [H+])

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15
Q

how is uncompensated respiratory acidosis indicated?

A

pH < 7.35 and PCO2 > 45 mmHg

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16
Q

where does respiratory acidosis sit on the davenport diagram?

A

top left

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17
Q

what system compensates for respiratory acidosis?

A

since respiratory system is the cause- renal system must compensate

18
Q

how does the renal system compensate for respiratory acidosis?

A
  • H+ secretion is stimulated
  • All filtered HCO3- is reabsorbed (i.e. no HCO3- excretion)
  • H+ continues to be secreted and generates titratable acid (TA) and NH4+
  • Acid is excreted and “new” HCO3- is added to the blood
19
Q

why does the [HCO3-] rise in respiratory acidosis?

A

(a) as a result of the disorder (b) as a result of the renal compensation

20
Q

what does correction of respiratory acidosis require?

A

requires lowering PCO2 by restoration of normal ventilation

21
Q

what is respiratory alkalosis?

A

Excessive removal of CO2 by the body e.g. hyperventilation

22
Q

How do these disruptions to ventilation cause respiratory alkalosis?

A

-Excessive CO2 removal drives equilibrium to the left and so Both [H+]p and [HCO3-]p fall

23
Q

where does respiratory alkalosis sit on the davenport diagram?

A

bottom right

24
Q

How does the renal system compensate for respiratory alkalosis?

A
  • The H+ secretion is insufficient to reabsorb the filtered HCO3-, even though the load is lower than normal
  • HCO3- is excreted and urine is alkaline
  • No titratable acid (TA) and NH4+ is formed, so no “new” HCO3- is generated
25
Q

what is the overall compensation and correction by the renal system for respiratory alkalosis?

A
  • Renal compensation further lowers [HCO3-]p

- Correction requires the restoration of normal ventilation

26
Q

what is metabolic acidosis?

A

Excess H+ from any source other than CO2 e.g. ingestion of acids

27
Q

how is Uncompensated respiratory alkalosis is indicated?

A

pH > 7.45 and PCO2 < 35 mmHg

28
Q

how does metabolic acidosis effect [HCO3-] p?

A

[HCO3-]p is depleted as a result of buffering excess H+ or loss of HCO3- from the body

29
Q

how is uncompensated metabolic acidosis indicated?

A

pH < 7.35, [HCO3-]p is low

30
Q

where is metabolic acidosis found on the davenport diagram?

A

bottom left

31
Q

what compensates for metabolic acidosis?

A

The respiratory system is not the cause so can participate in compensation

32
Q

How does the respiratory system compensate for metabolic acidosis?

A
  • A decrease in plasma pH stimulates peripheral chemoreceptors
  • Ventilation is quickly increased and more CO2 is blown off
  • [H+]p is lowered raising pH towards normal
  • [HCO3-]p is also lowered
33
Q

what is the correction for metabolic acidosis?

A
  • Filtered HCO3- is very low and very readily reabsorbed
  • H+ secretion continues and produces TA & NH4+ to generate more “new” HCO3-
  • The acid load is excreted (urine is acidic) and [HCO3-]p is restored
  • Ventilation can then be normalised
34
Q

why is respiratory compensation in metabolic acidosis essential?

A

Acid load cannot be excreted immediately

35
Q

what is metabolic alkalosis?

A

Excessive loss of H+ from the body e.g. loss of HCl from the stomach

36
Q

how does metabolic alkanosis effect [HCO3-] p?

A

As a result of loss of H+ or addition of base, [HCO3-]p rises

37
Q

what is uncompensated metabolic alkalosis indicated by?

A

pH > 7.45, [HCO3-]p is high

38
Q

where does metabolic alkalosis sit on the davenport diagram?

A

top right

39
Q

what is the respiratory compensation for metabolic alkalosis/

A
  • Increased pH slows ventilation (peripheral chemoreceptors)
  • CO2 retained, PCO2 rises
  • [H+]p rises, lowering pH
  • [HCO3-]p also rises further
40
Q

what is the correction for metabolic alkalosis?

A
  • Filtered HCO3- load is so large compared to normal that not all of the filtered HCO3- is reabsorbed
  • No TA or NH4+ is generated
  • HCO3- is excreted (urine is alkaline)
  • [HCO3-]p falls back towards normal

Renal physiology (8 decks)

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