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Resipiratory > Session 5 - Acid-Base Balance > Flashcards

Session 5 - Acid-Base Balance Flashcards

1
Q

What pH range should blood plasma normally be maintained at?

A

7.35 - 7.45

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2
Q

What defines acidaemia and alkalaemia?

A

Acidaemia - Plasma pH less than 7.35

Alkalaemia - Plasma pH greater than 7.45

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3
Q

What are the effects to the plasma and cells of alkalaemia?

A

Alkalaemia lowers free calcium, by causing Ca2+ ions to come out of solution.
This can increase neuronal excitability and cause tetany.

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4
Q

How does alkalaemia cause Ca2+ to come out of solutin / blood Ca2+ to lower?

A
  • pH Increases, so H+ <
  • Albumin and other blood proteins become anions (lose H+).
  • Ca2+ binds to these proteins
    (In severe alkalaemia)
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5
Q

Which is more dangerous? Alkalaemia or Acidosis?

A

Alkalosis can be more serious.

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6
Q

What are the mortalities of a plasma pH 7.55, and 7.65?

A
  1. 55 = 45% mortality

7. 65 = 80% mortality

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7
Q

What are the effects of acidaemia on the body?

A
  • Increase plasma potassium ion concentration.
    (effects excitability, particularly cardiac muscle, can cause arrythmia)
  • Increased H+ can affect enzymes (denature)
    (effects muscle contractility, glycolysis, liver etc)
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8
Q

When are the effects of acidaemia a) severe, and b) life threatening?

A

Severe = pH <7.1

Life threatening = pH <7.0

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9
Q

Which factors in the body control pH?

A
  • Ratio of [HCO3] to pCO2.
  • pCO2 defined by respiration.
  • [HCO3-] controlled by kidneys
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10
Q

Why does metabolic acid production not deplete HCO3-?

A
  • Kidneys recover all filtered HCO3-
  • Proximal tubule makes HCO3- from amino acids, putting NH4+ in urine.
  • Distal tubule makes bicarbonate from CO2 and water, H+ is buffered by phosphate and ammonia in urine.
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11
Q

How are bicarbonate ions produced in the proximal tubule?

A

Glutamin > a-ketoglutarate
which: produces bicarbonate and ammonium.
Bicarbonate enters ECF, ammonium enters lumen (urine).

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12
Q

How are hydrogen ions removed from the body, without being reformed into water and moving back into tubule cells?

A
  • H+ ions actively secreted
  • H+ buffered by ammonia and phosphate, producing NH4+ and H2PO4- in urine.
  • This prevents CO2 from being reformed from bicarbonate, and bicarbonate re-enters the plasma.
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13
Q

Why is buffering of the H+ in urine important?

A

Stops urine becoming too acidic.

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14
Q

What is the major adaptive response to increased acid load in healthy people?

A

Excretion of ammonium.
- Ammonium generation from glutamine can be increased.

  • NH3 moves freely into lumen and through interstitium.
  • H+ actively pumped into lumen in DCT + CT.
  • H+ combines with NH3, making NH4+
    this is trapped in lumen, and excreted.
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15
Q

What is the minimum pH of urine?

A

4.5

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16
Q

What is the total acid excretion in urine per day?

A

50-100mmol H+ per day

17
Q

How does acidosis and alkalosis affect potassium?

A

Acidosis = >H+

  • Potassium ions move OUT of cells, H+ moves in
  • Decreased potassium excretion in distal nephron

Alkalosis =

18
Q

How does hypokalaemia affect pH?

A
  • Hypokalaemia makes H+ ions move into cells (tubular cell pH more acidic)
  • Favours H+ excretion and HCO3- recovery

Metabolic Alkalosis

19
Q

How does hyperkalaemia affect tubule pH, and plasma pH?

A
  • Hyperkalaemia - H+ move out of cells. (makes tubular cell pH more alkaline)
  • Favours HCO3- excretion

Metabolic acidosis

20
Q

What is uncompensated respiratory acidosis?

A

Hypoventilation (hypercapnia)
Fall in pH, increases pCO2.
Causes acidosis (acidaemia)
NORMAL HCO3-

21
Q

What is uncompensated respiratory alkalosis?

A

Hyperventilation (hypocapnia)
RISE in pH, decreased pCO2 (fewer H+ ions)
Alkalosis (alkalaemia)
Nomal HCO3-

22
Q

How can the kidneys compensate against respiratory acidosis or alkalosis?

A 
Acidosis = Increase HCO3-
Alkalosis = Decrease HCO3-
23
Q

What is metabolic acidosis?

A

When tissues produce acid, which reacts with, and removes HCO3-.
Fall in HCO3- and thus pH.

24
Q

Why is there no change in pCO2 with metabolic acidosis?

A

The extra CO2 produced is breathed off at lungs.

25
Q

What is the anion gap?

A

The measured difference between the main cations and anions.

([Na+] + [K+]) - ([Cl-] + [HCO3-]

26
Q

What is the normal anion gap? When does it change?

A

10-18mmol/L

Change if bicarbonate is replaced by other anions.

27
Q

In renal causes of acidosis, why is the anion gap unchanged?

A
  • Not making enough HCO3-, but this will be replaced by Cl-
28
Q

How is metabolic acidosis compensated?

A

Peripheral chemoreceptors detect stimulation of ventilation

Low HCO3-
Lowered pCO2
Nearer normal pH

29
Q

Why can metabolic alkalosis not be corrected for by breathing?

A

Reducing ventilation would impair pO2, which needs to be maintained for perfusion of tissues.

30
Q

Which conditions can lead to respiratory acidosis?

A

Type 2 Respiratory failure

  • Low PO2, high pCO2
  • alveoli not properly ventilated

COPD, Asthma, drug overdose, neuromuscular disease

31
Q

Which conditions can lead to respiratory alkalosis?

A

Hyperventilation

  • Anxiety/ panic attacks
  • Low pCO2, >pH

Hyperventilation in response to long term hypoxia
- Low pCO2, initial rise in pH which is compensated for by fall in HCO3-

32
Q

Which conditions can lead to metabolic acidosis?

A

If anion gap is INCREASED - must be metabolic.
-Keto-acidosis (diabetes)

  • Lactic acidosis (exercise exhaustion, low tissue perfusion)
  • Uraemic acidosis (Advanced renal failure)
33
Q

What causes uraemic acidosis in advanced renal failure?

A

Reduced acid secretion in kidneys.

Build up of phosphate, sulphate and urate in blood.

34
Q

Which conditions lead to metabolic acidosis with a normal anion gap?

A
  • Renal tubular acidosis (rare)
    problems with transport mechanisms in tubules.
  1. Type 1 RTA - inability to pump out H+
  2. Type 2 RTA - problems with HCO3- reabsorption.
  • Severe persistent diarrhoea, through loss of HCO3-
    (replaced by Cl- so gap unaltered)
35
Q

What happens to K+ in non renal acidosis?

A

Increased reabsorption of K+.
Movement of K+ out of cells.
> HYPERKALAEMIA

(in diabetic ketoacidosis, may be total body depletion of K+)

36
Q

Which conditions can lead to metabolic alkalosis?

A
  • Severe prolonged vomiting (stomach makes lots of HCO3-)
  • Potassium depletion
  • Some diuretics (loop/ thiazide)
37
Q

How is metabolic alkalosis corrected?

A

> pH causes fall in H+ excretion. Reduced HCO3- recovery.

38
Q

In volume depletion, what happens in metabolic alkalosis?

A

Capacity to lose HCO3- is reduced, due to high rate of Na+ recovery.
Recovering Na+ favours H+ excretion and HCO3- recovery.

39
Q

How can metabolic alkalosis cause hypokalaemia?

A

Less H+ excreted at nephrons, causes more K+ to be excreted.
Alkalosis causes K+ to move INTO cells.
causes hypokalaemia

Resipiratory (9 decks)

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