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Renal Physiology > K8 - Acid Base Balance II- Whole body acid-base balance > Flashcards

K8 - Acid Base Balance II- Whole body acid-base balance Flashcards

1
Q

When will a person have a normal acid- base balance?

A
  1. Plasma pH close to 7.4
  2. [HCO3-]p close to 25 mol/l
  3. Arterial PCO2 close to 40mmHg
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2
Q

what is compensation?

A

if normal acid-base balance is disrupted then priority is to restore pH to 7.4 irrespective of bicarbonate levels and partial pressure of CO2

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3
Q

what is correction?

A

restoration of pH and bicarbionate and PCO2 to normal

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4
Q

Name two disturbances of respiratory origin

A
  • respiratory acidosis (plasma pH falls)

- respiratory alkalosis (plasma pH rises)

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5
Q

Name two Disturbances of non-respiratory origin

A
  • metabolic acidosis (plasma pH falls)

- metabolic alkalosis (plasma pH rises)

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6
Q

how the body initally limits pH changes?

A
  • immediate dilution of acid or base in ECF
  • blood buffers
  • buffers in the ECF - bicarbonate
    stores deplete very quickly so kidney has to rectify the problem
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7
Q

What can measure pH and PCO2?

A

A blood-gas analyser

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8
Q

What is the name for the diagram which shows [HCO3-]p and plasma pH?

A

Davenport Diagram

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9
Q

What is respiratory acidosis?

A

retention of CO2 by the body

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10
Q

Give 5 examples of respiratory acidosis

A
  • chronic bronchitis
  • chronic emphysema
  • airway restriction (bronchial asthma, tumour)
  • chest injuries
  • respiratory depression
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11
Q

what causes respiratory acidosis?

A

CO2 retention drives equilibrium to the right

CO2 + H2O >< H2CO3 >< H+ + HCO3-

so both [H+]p and [HCO3-]p rise and the increases [H+] results in acidosis

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12
Q

what range of values does respiratory acidosis occur in?

A

pH < 7.35 and PCO2 > 45 mmHg

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13
Q

Is there extracellular buffering in respiratory disorders?

A

virtually none

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14
Q

What stimulates H+ secretion into the filtrate to compensate for respiratory acidosis?

A

CO2 retention stimulates H+ secretion into the filtrate

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15
Q

Describe the events that happen after H+ secretion is stimulated for respiratory acidosis compensation?

A
  • all filtered HCO3- is reabsorbed
  • H+ continues to be secreted and generates titratable acid (TA) and NH4+
  • acid is excreted and “new” HCO3- is added to the blood
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16
Q

Why does [HCO3-]p rise?

A
  • as a result of the disorder

- as a result of the renal compensation

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17
Q

What is correction process in respiratory acidosis?

A

Lowering PCO2 by restoration of normal ventilation

18
Q

how does respiratory acidosis appear on davenport diagram?

A

pH too low and bicarbonate too high

19
Q

What is respiratory alkalosis?

A

Excessive removal of CO2 by the body

20
Q

When would respiratory alkalosis occur? 3 examples

A
  • low inspired PO2 at altitude
  • hyperventilation (causes include fever, brainstem damage)
  • hysterical over breathing
21
Q

What does respiratory alkalosis do to the buffer equation?

A

drives equilibrium to the left resulting in [H+]p and [HCO3-]p decrease

22
Q

What indicates respiratory alkalosis?

A

pH> 7.45

PCO2< 35mmHg

23
Q

what is the compensatory mechanism for respiratory alkalosis?

A
  1. excessive removal of CO2 reduces H+ secretion into the filtrate
  2. H+ secretion is insufficient to reabsorb the filtered bicarbonate
  3. bicarbonate is excreted into the urine
  4. no titratable acid or NH4+ is produced
24
Q

What does renal compensation for respiratory alkalosis do to [HCO3-]p?

A

Lowers [HCO3-]p

25
Q

What does correction require in respiratory alkalosis?

A

restoration of normal ventilation

26
Q

how does respiratory acidosis appear on davenport diagram?

A

pH too high and bicarbonate too low

27
Q

What is metabolic acidosis ?

A

Excess H+ from any source other than CO2

28
Q

Give 3 examples of metabolic acidosis

A
  • ingestion of acids or acid- producing foodstuffs
  • excessive metabolic production of H+ (lactic acid during exercise or ketoacidosis)
  • excessive loss of base from the body
29
Q

In metabolic acidosis what is depleted as a result of buffering excess H+ or loss of HCO3- from the body?

A

[HCO3-] from the body

30
Q

What is metabolic acidosis indicated by?

A

pH less than 7.35

[HCO3-]p is low

31
Q

Explain respiratory compensation for metabolic acidosis

A
  1. decrease in plasma
  2. pH stimulates peripheral chemoreceptors
  3. ventilation is quickly increased and more carbon dioxide is blown off
  4. H+ and bicarbonate both lowered as there isn’t any carbon dioxide to make them
32
Q

Explain 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
33
Q

how does metabolic acidosis appear on davenport diagram?

A

pH to low and bicarbonate too low

34
Q

What does metabolic alkalosis result in?

A

Excessive loss of H+ from the body

35
Q

Give 3 examples of metabolic alkalosis

A
  • loss of HCL from the stomach (vomiting)
  • ingestion of alkali or alkali- producing foods (ingestion of NaHCO3 as an antacid, though not a problem with modern antacids)
  • aldosterone hypersecretion (causes stimulation of Na+/H+ exchange at the apical membrane of the tubule; acid secretion)
36
Q

In metabolic alkalosis what happens to [HCO3-]p as a result of loss of H+ or addition of base?

A

[HCO3-]p rises

37
Q

What is uncompensated metabolic alkalosis indicated by?

A
  • pH > 7.45

- [HCO3-]p high

38
Q

Explain Respiratory compensation for metabolic alkalosis

A
  1. Increased pH slows ventilation
  2. CO2 retained, PCO2 rises
  3. [H+]p rises, lowering pH
  4. [HCO3-]p also rises further
39
Q

In metabolic alkalosis why is not all of the filtered HCO3- reabsorbed?

A

Because HCO3- is so large compared to normal

40
Q

Explain the renal correction for metabolic alkalosis

A
  • filtered bicarbonate load is so large compared to normal that not all the filtered bicarbonate is reabsorbed
  • no titrateable acid or NH4+ is generated
  • bicarbonate is excreted (alkaline urine)
  • bicarbonate levels fall back to normal

Renal Physiology (8 decks)

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