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19. Integrative > 1. Acid-Base Balance > Flashcards

1. Acid-Base Balance Flashcards

1
Q

What range should plasma pH be within?

A

7.35-7.45

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2
Q

What is the concentration of H+ in the plasma?

A

Low and tightly controlled 44.5-35.5 nmol.l^-1.

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3
Q

What is alkalaemia?

A

Plasma pH > 7.45

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4
Q

What is acidaemia?

A

Plasma pH < 7.35

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5
Q

What is the effect of alkalaemia on Ca2+ and therefore neuronal excitability?

A

Lowers free calcium by causing Ca2+ to come out of solution. It increases excitability.

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6
Q

What are the effects of pH > 7.45?

A

Paraesthesia and tetany.

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7
Q

What is the effect of acidaemia on K+?

A

Increases plasma potassium ion concentration.

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8
Q

What are the effects of increased H+ concentration?

A

Denatured proteins (affecting enzymes) so muscle contractility, glycolysis, and hepatic function are altered.

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9
Q

What is the purpose of the CO2/HCO3- buffer system?

A

To minimise changes in pH by buffering H+ ions.

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10
Q

How do CO2, HCO3-, and H+ interact?

A

CO2 reacts with water –> HCO2- + H+ - this is a reversible reaction.

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11
Q

What is pCO2 determined by?

A

Respiration - controlled by chomoreceptors.

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12
Q

What is HCO3- concentration controlled by?

A

Kidneys.

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13
Q

How does high pCO2 affect pH?

A

Makes it more acidic, more H+ made.

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14
Q

Where is hydrogen carbonate in plasma made?

A

In red blood cells.

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15
Q

How does HCO3- affect plasma pH?

A

Large concentration nearly stops all CO2 reacting so makes pH alkaline as it uses up the H+.

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16
Q

What is the Henderson-Hasselbach equation?

A

pH = pK + Log ([HCO3-]/(pCO2 x 0.23))

17
Q

How is HCO3- controlled by the kidneys?

A

It’s filtered at the glomerulus and recovered in PCT. H+ excretion is linked to Na+ entry in PCT and H+ reacts with HCO3- to make CO2. It’s converted back to HCO3- in cells.

18
Q

What is a key renal response to acidaemia?

A

Excretion of ammonium.

19
Q

How does hyperkalaemia affect pH?

A

Makes it acidotic as K+ move out of cells and there’s decreased excretion in distal nephron.

20
Q

How does hypokalarmia affect pH?

A

Makes it alkalotic, K+ moves into cells and enhances excretion in distal nephron.

21
Q

How does ventilation affect acid base balance? (Think at either extreme)

A

Hypoventilation -> hypercapnia -> fall in plasma pH = respiratory acidosis.
Hyperventilation -> hypocapnia -> increased pH = respiratory alkalosis.

22
Q

What are the characteristics of respiratory acidosis?

A

High pCO2, normal HCO3-, low pH.

23
Q

What are the characteristics of respiratory alkalosis?

A

Low pCO2, normal HCO3-, raised pH.

24
Q

How does the kidneys compensate for respiratory acidosis and alkalosis?

A

Acidosis - increase HCO3-. Alkalosis - decrease HCO3-.

25
Q

How long does it take for the kidneys to compensate for respiratory acidosis or alkalosis?

A

2-3 days.

26
Q

What are the characteristics of compensated respiratory acidosis?

A

High pCO2, raised HCO3-, normal pH.

27
Q

What are the characteristics of compensated respiratory alkalosis?

A

Low pCO2, lowered HCO3-, normal pH.

28
Q

What is the effect on pH of metabolic acid?

A

Reacts with and removes HCO3- so there’s a fall and a fall in pH = metabolic acidosis.

29
Q

What is the anion gap?

A

Difference between measured cations and anions.

30
Q

How is the anion gap calculated?

A

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

31
Q

What increases the anion gap?

A

Increases - if HCO3- is replaced by other anions, e.g. in metabolic acidosis.

32
Q

What are the characteristics of metabolic acidosis?

A

Normal pCO2, low HCO3-, low pH, increased anion gap is HCO3- is replaced by another organic anion or normal if replaced by Cl-.

33
Q

How is metabolic acidosis compensated for?

A

Peripheral chemoreceptors detect pH drop -> stimulate ventilation -> decreased CO2.

34
Q

Which conditions cause respiratory acidosis?

A

Type 2 respiratory failure (alveoli aren’t properly ventilated so low pO2, high pCO2) - COPD, severe asthma, drug overdose, neuromuscular disease.

35
Q

Which conditions lead to respiratory alkalosis?

A

Hyperventilation (anxiety, panic attacks) in acute settings. Hyperventilation in long-term hypoxia - type 1 respiratory failure.

36
Q

Which conditions lead to metabolic acidosis with increased anion gap?

A

Keto-acidosis, lactic acidosis, uraemic acidosis.

37
Q

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

A

Renal tubular acidosis, persistent diarrhoea.

38
Q

Which conditions lead to metabolic alkalosis?

A

Prolonged vomiting or mechanical drainage of stomach, potassium depletion, diuretics.

19. Integrative (7 decks)

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