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Renal > Acid-Base Balance II > Flashcards

Acid-Base Balance II Flashcards

1
Q

When would a person be considered to be of normal acid-base balance?

A

Plasma pH close to 7.4 (range 7.35-7.45)
[HCO3-]p close to 25 mmol/l (range 23-27)
Arterial PCO2 close to 40mmHg (range 35-45)

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2
Q

What is compensation?

A

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, [HCO3-]p and PCO2 to normal

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4
Q

What is the first priority if normal acid-base balance is disturbed?

A

To restore pH

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5
Q

What acid-base disturbances cause plasma pH to fall?

A

Respiratory acidosis and metabolic acidosis

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6
Q

What acid-base disturbances cause plasma pH to rise?

A

Respiratory alkalosis and metabolic alkalosis

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7
Q

What occurs in immediate buffering of pH change?

A

Immediate dilution of the acid or the base in ECF

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8
Q

What carries out the immediate buffering of pH change?

A

Blood buffers or buffers in the ECF

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9
Q

What is the issue with immediate buffering of pH change?

A

Response is very quick but the buffer stores are quickly depleted = kidney must rectify stores

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10
Q

How is blood-gas analysis carried out?

A

A blood gas analyser can measure pH and PCO2

[HCO3-]p can then be calculated

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11
Q

What is used to plot the results of blood-gas analysis?

A

A Davenport diagram

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12
Q

What is respiratory acidosis?

A

Retention of CO2 by the body

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13
Q

What are some causes of respiratory acidosis?

A

Chronic bronchitis, chronic emphysema, airway restriction, chest injuries, respiratory depression

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14
Q

What does CO2 retention due to respiratory acidosis do to the equilibrium?

A

Drives it to the right = both [H+]p and [HCO3-] rise

Increased [H+] results in acidosis

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15
Q

What is uncompensated respiratory acidosis?

A

pH < 7.35 AND PCO2 > 45 mmHg

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16
Q

How are respiratory disorders compensated for?

A

Virtually no extracellular buffering in respiratory disorders so renal system must compensate

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17
Q

What drives H+ secretion by the kidney?

A

PCO2 = CO2 retention stimulates H+ secretion into the filtrate

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18
Q

How does the renal compensate in respiratory acidosis?

A

H+ secretion stimulated
All filtered HCO3- reabsorbed
H+ continues to be secreted and generates titratable acid and NH4+
Acid secreted and new HCO3- is added to blood

19
Q

What causes [HCO3-] to rise in respiratory acidosis?

A

Both the disorder and the renal compensation

20
Q

What does correction of respiratory acidosis and alkalosis require?

A

Restoration of normal ventilation

21
Q

What is respiratory alkalosis?

A

Excessive removal of CO2 by the body

22
Q

What are some causes of respiratory alkalosis?

A

Low inspired PO2 at altitude, hyperventilation, hysterical overbreathing

23
Q

What does respiratory alkalosis do to the equilibrium?

A

Drives it to the left = [H+]p and [HCO3-]p fall

Decreased [H+]p results in alkalosis

24
Q

What is uncompensated respiratory alkalosis?

A

pH > 7.45 AND PCO2 < 35 mmHg

25
Q

What effect does respiratory alkalosis have on the kidney?

A

Excessive removal of CO2 reduces H+ secretion into the tubule

26
Q

Why does respiratory alkalosis cause alkaline urine?

A

H+ secretion insufficient to reabsorb filtered HCO3- = HCO3- excreted in urine

27
Q

How does the renal system compensate for respiratory alkalosis?

A

HCO3- excreted in urine

No titratable acid or NH4+ produced so there is no new HCO3- generated

28
Q

What is metabolic acidosis?

A

Excess H+ from any source other than CO2

29
Q

What are some cause of metabolic acidosis?

A

Ingestion of acid/acid producing foods
Excessive metabolic production of H+ (e.g DKA)
Excessive loss of base (e.g diarrhoea)

30
Q

What cause [HCO3-] depletion in metabolic acidosis?

A

Buffering excess H+ or loss of HCO3- from the body

31
Q

What is uncompensated metabolic acidosis?

A

pH < 7.35, [HCO3-]p is low

32
Q

What stimulates the respiratory system in metabolic acidosis and alkalosis?

A

Peripheral chemoreceptors = decrease/increase in plasma pH respectively

33
Q

How does the respiratory system compensate for metabolic acidosis?

A

Ventilation is quickly increased and more CO2 is blown off, [H+]p is lowered raising the pH towards normal, [HCO3-]p is also lowered

34
Q

Why is respiratory compensation essential in correcting metabolic acidosis?

A

Acid load cannot be excreted immediately

35
Q

When does ventilation return to normal in metabolic acidosis?

A

Once acid load is excreted (acidic urine) and [HCO3-]p is restored

36
Q

How is metabolic acidosis corrected?

A

Filtered HCO3- is very low and very readily reabsorbed
H+ secretion continues and produces titratable acid and NH4+ to generate more new HCO3-
Acid excreted in urine

37
Q

What is metabolic alkalosis?

A

Excessive loss of H+ from body = less common than metabolic acidosis

38
Q

What are some causes of metabolic alkalosis?

A

Loss of HCl from stomach (e.g vomiting), ingestion of alkali/alkali-producing foods, hypersecretion of aldosterone

39
Q

What causes the rise in [HCO3-]p in metabolic alkalosis?

A

H+ loss or addition of base

40
Q

What is uncompensated metabolic alkalosis?

A

pH > 7.4, [HCO3-]p is high

41
Q

How does the respiratory system compensate for metabolic alkalosis?

A

Increased pH slows ventilation = CO2 retained, PCO2 rises

[H+]p rises which lowers pH and [HCO3-] rises further

42
Q

Why can’t all of the filtered HCO3- be reabsorbed in metabolic alkalosis?

A

Filtered HCO3- load is so large compared to normal that there is too much to completely reabsorb

43
Q

How is metabolic alkalosis corrected?

A

No titratable acid or NH4+ generated so no new HCO3- produced, HCO3- is excreted in urine (alkaline urine), [HCO3-]p falls back towards normal

Renal (36 decks)

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