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ESA 3- Urinary System > Control of Acid/Base > Flashcards

Control of Acid/Base Flashcards

1
Q

What is the normal range of plasma pH?

A

7.38-7.46

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2
Q

What is the normal H+ concentration of the plasma?

A

37-43nmol/L

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3
Q

When are the effects of acidaemia severe?

A

Below pH 7.1

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4
Q

When are the effects of acidaemia life threatening?

A

Below pH 7.0

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5
Q

What are the effects of acidaemia?

A
  • Reduced enzyme function
  • Reduced glycolysis
  • Reduced cardiac and skeletal muscle contractility
  • Reduced hepatic function
  • Increased plasma potassium
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6
Q

What is the effect of alkalaemia on calcium salts?

A

Reduces their solubility

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7
Q

What is the result of the reduced solubility of calcium salts in alkalaemia?

A

Means that free Ca2+ leaves the ECF

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8
Q

How does free Ca2+ leave the ECF?

A

Binds to bone and protein

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9
Q

What is the result of free Ca2+ leaving the ECF in alkalaemia?

A

Results in hypocalcaemia

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10
Q

What is the effect of hypocalcaemia?

A

Increases the excitability of nerves

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11
Q

What happens at pH > 7.45?

A

Parasthesia

Tetany

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12
Q

What is tetany?

A

Uncontrolled muscle contractions

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13
Q

What happens at pH > 7.55?

A

45% mortality

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14
Q

What happens at pH > 7.65?

A

80% mortality

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15
Q

Describe the H+ ion concentration of the ECF?

A

It is very low

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16
Q

What is the result of the H+ concentration of the ECF being very low?

A

The addition of small amounts of acid changes the concentration and therefore the pH dramatically

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17
Q

What prevents the addition of small amounts of acid to the ECF changing the pH dramatically?

A

The carbon dioxide/hydrogen carbonate system acts as an important buffer for the H⁺ ions

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18
Q

What reaction occurs in the carbon dioxide/hydrogen carbonate system?

A

H2O+CO2 H2CO3 (carbonic acid) H+ + HCO3-

H+ reacts with OH to produce water

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19
Q

What is the extent to which the reversible reaction proceeds in the carbon dioxide/hydrogen carbonate system determined by?

A

The ratio of pCO2 of plasma to [HCO3-]

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20
Q

What is the pCO2 of plasma controlled by?

A

Lungs

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21
Q

What is HCO3- created by?

A

Largely RBC

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22
Q

What is the concentration of plasma HCO3- controlled by?

A

Kidneys

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23
Q

What is the normal [HCO3-]:pCO2 ratio?

A

20:1

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24
Q

What is the result of anything that alters the [HCO3-]:pCO2 ratio?

A

It also alters the pH

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25
Q

What happens in respiratory alkalaemia?

A

As hyperventilation leads to hypocapnia (fall in pCO2), the ratio is altered and pH will rise. There is more than 20x the amount of HCO3- than CO2, so relatively more H+ ions are buffered, causing the pH increase

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26
Q

What pH is considered respiratory alkalaemia?

A

> 7.45

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27
Q

Why must is be respiratory alkalaemia if breathing quickly?

A

If lungs were fine, breathing would be slowed to raise pCO2

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28
Q

What happens in respiratory acidaemia?

A

Hypoventilation leads to hypocapnia. The ratio is altered and pH will fall. There is less than 20x the amount of HCO3- than CO2, so relatively less H+ ions are buffered, causing the pH to decrease

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29
Q

What pH is considered respiratory acidaemia?

A

<7.35

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30
Q

Why must it be respiratory acidaemia if breathing slowly?

A

Because if lungs were fine, breathing would be sped up to lower pCO2

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31
Q

What can compensate respiratory alkalosis or acidosis?

A

Changes in [HCO3-] controlled by the kidney

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32
Q

Why can respiratory acidosis or alkalosis be compensated for by the kidney?

A

Because the pH is controlled by the ratio, and not absolute values.

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33
Q

How does the kidney control [HCO3-]?

A

Variable renal excretion/production

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34
Q

What does the kidney do if pCO2 rises?

A

[HCO3-] rises proportionally to restore pH

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35
Q

What does a rise in [HCO3-] caused by the kidney compensate for?

A

Respiratory acidosis

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36
Q

What does the kidney do if pCO2 falls?

A

[HCO3-] falls proportionally to restore pH

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37
Q

What does a fall in [HCO3-] caused by the kidney compensate for?

A

Respiratory alkalosis

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38
Q

What metabolic processes produce H+ ions?

A

Metabolism of amino acids or the production of ketones

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39
Q

What happens to metabolically produced H+ ions?

A

They react with HCO3- to produce CO2 in venous blood

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40
Q

What happens to the CO2 produced by the reaction of metabolically produced H+ ions?

A

It is breathed out through the lungs

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41
Q

What is the result of the breathing out of the CO2 production by the reaction of metabolically produced H+ ions?

A

It gives a directly proportional (1mmol acid:1mmol HCO3-) reduction in arterial HCO3-

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42
Q

What is the result of the directly proportional reduction in arterial HCO3- caused by metabolically produced H+?

A

It alters the [HCO3-]:pCO2 ratio, meaning that less than 20x the amount of HCO3- than CO2. Relatively less H+ ions are buffered, causing a pH decrease

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43
Q

What is it called when metabolically produced H+ ions cause a pH decrease?

A

Metabolic acidosis

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44
Q

What pH is considered metabolic acidosis?

A

<7.35

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45
Q

What can compensate for metabolic acidosis or alkalosis?

A

The lungs

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46
Q

Why can the lungs compensate for metabolic acidosis or alkalosis?

A

As pH depends on the ratio of [HCO3-]:pCO2, so the lungs can change pCO2.

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47
Q

What do the lungs normally do regarding CO2?

A

Keep it within tight limits

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48
Q

How is CO2 normally kept within tight limits by the lungs?

A

By central chemoreceptors

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49
Q

How do changes in plasma pH drive changes in pCO@?

A

Via the peripheral chemoreceptors

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50
Q

What happens if [HCO3-] falls?

A

pCO2 is lowered proportionally by increasing ventilation

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51
Q

What does the increase in ventilation due to a fall in [HCO3-] compensate for?

A

Metabolic acidosis

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52
Q

What happens if [HCO3-] rises?

A

pCO2 may be slightly raised by reducing ventilation

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53
Q

What does the reduction in ventilation due to a increase in [HCO3-] compensate for?

A

Metabolic alkalosis, although only partially

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54
Q

What happens to pH in respiratory acidosis?

A

Decreased

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55
Q

What happens to pCO2 in respiratory acidosis?

56
Q

Why is pCO2 increased in respiratory acidosis?

A

Hypoventilation

57
Q

What happens to [HCO3-] in respiratory acidosis?

58
Q

What happens to pO² in respiratory acidosis?

59
Q

What happens to pH in compensated respiratory acidosis?

A

pH decreased or normal

60
Q

What happens to pCO2 in compensated respiratory acidosis?

61
Q

What happens to [HCO3-] in compensated respiratory acidosis?

62
Q

What happens to pO2 in compensated respiratory acidosis?

63
Q

What is happening in compensated respiratory acidosis?

A

Kidneys have increased [HCO3-]. This causes increases in buffering of H+ ions caused by increased pCO2.

64
Q

What happens to pH in respiratory alkalosis?

65
Q

What happens to pCO2 in respiratory alkalosis?

66
Q

Why does pCO2 decrease in respiratory alkalosis?

A

Hyperventilation

67
Q

What happens to [HCO3-] in respiratory alkalosis?

68
Q

What happens to pO2 in respiratory alkalosis?

A

Normal or increased

69
Q

What happens to pH in compensated respiratory alkalosis?

A

Increased or normal

70
Q

What happens to pCO2 in compensated respiratory alkalosis?

71
Q

What happens to [HCO3-] in compensated respiratory alkalosis?

72
Q

What happens to pO2 in compensated respiratory alkalosis?

73
Q

What is happening in compensated respiratory alkalosis?

A

Kidneys have decreased [HCO3-], decreasing buffering of H+ ions

74
Q

What happens to pH in metabolic acidosis?

75
Q

What happens to pCO2 in metabolic acidosis?

76
Q

What happens to [HCO3-] in metabolic acidosis?

77
Q

What happens to pO2 in metabolic acidosis?

78
Q

What happens to the anion gap in metabolic acidosis?

79
Q

What is happening in metabolic acidosis?

A

Decreased [HCO3-] means less buffering of H+ ions

80
Q

Why is here an increase in the amnion gap in metabolic acidosis?

A

Increase in unmeasured anions because anions associated with increase in H+ has taken HCO3- places

81
Q

What happens to pH in compensated metabolic acidosis?

A

Decreased or normal

82
Q

What happens to pCO2 in compensated metabolic acidosis?

83
Q

What happens to [HCO3-] in compensated metabolic acidosis?

84
Q

What happens to pO2 in compensated metabolic acidosis?

A

Increased or unchanged

85
Q

What happens to the anion gap in compensated metabolic acidosis?

86
Q

What is happening in compensated metabolic acidosis?

A

Increased respiratory rate is leading to hypocapnia and therefore raised pH

87
Q

What happens to the pH in metabolic alkalosis?

88
Q

What happens to pCO2 in metabolic alkalosis?

89
Q

What happens to [HCO3-] in metabolic alkalosis?

90
Q

What happens to pO2 in metabolic alkalosis?

91
Q

What is happening in metabolic alkalosis?

A

Increased [HCO3-] means increased buffering of H+

92
Q

What happens to pH in compensated metabolic alkalosis?

A

It increases or is normal

93
Q

What happens to pCO2 in compensated metabolic alkalosis?

94
Q

What happens to [HCO3-] in compensated metabolic alkalosis?

95
Q

What happens to pO2 in compensated metabolic alkalosis?

A

Decreased or unchanged

96
Q

What is happening in compensated metabolic alkalosis?

A

Decreased respiratory rate, so hypercapnia, so decreased pH

97
Q

How is HCO3- reabsorbed in the PCT?

A
  • 3Na/2K-ATPase sets up Na+ concentration gradient in PCT cells
  • H+ ions are pumped out of the apical membrane up their concentration gradient in exchange for the inward movement of Na down its concentration gradient
  • H+ reacts with filtered HCO3-, producing CO2, which enters the cell and reacts with water to produce H+ ions
  • H+ is quickly exported, recreating HCO3-, which crosses the basolateral membrane to enter the plasma
98
Q

What % of filtered HCO3- is reabsorbed in the PCT?

99
Q

Other than the PCT, where else is HCO3- reabsorbed?

A

In the TAL of the loop of Henle

100
Q

What % of filtered HCO3- is reabsorbed in the loop of Henle?

101
Q

How does the mechanism of HCO3- reabsorption in the loop of Henle compare to that in the PCT?

A

It is similar

102
Q

What has happened to HCO3- by the DCT?

A

Most/all of the filtered HCO3- has been recovered

103
Q

Is the Na+ gradient sufficient to drive H+ secretion in the DCT?

104
Q

What is the result of the Na+ gradient being insufficient to drive H+ reabsorption in the DCT?

A

H+ is pumped across the apical membrane by H+-ATPase

105
Q

What are the H+-ATPase pumps found in the DCT similar to?

A

Those found in the stomach

106
Q

What happens, regarding K+, when tubular cells export H+?

A

K+ is absorbed into the blood

107
Q

What is the result of K+ be absorbed into the blood when tubular cells export H+ in tubule lumen?

A

If you export a lot of H+, you will also absorb a lot of K+

108
Q

What is the result of the relationship between H+ exportation and K+ absorption?

A

Blood pH is linked to [K+]

109
Q

What is the minimum pH of urine?

110
Q

Is HCO3- found in urine?

111
Q

What is the result of HCO3- not being found in urine?

A

H+ is buffered by phosphate

112
Q

What kind of acid is phosphate?

A

Titratable

113
Q

What is meant by phosphate being a titratable acid?

A

It can freely gain H+ ions in an acid/base reaction

114
Q

What happens to the H+ in urine not buffered by phosphate?

A

It is attached to ammonia as ammonium

115
Q

What is metabolic acidosis associated with?

A

Hyperkalaemia

116
Q

Why is metabolic acidosis associated with hyperkalaemia?

A

As [K+] rises, the kidneys ability to reabsorb and create [HCO3-] is reduced. Hyperkalamia makes the intracellular pH alkaline, favouring HCO3- excretion

117
Q

What is metabolic alkalosis associated with?

A

Hypokalaemia

118
Q

Why is metabolic alkalosis associated with hypokalaemia?

A

Because it makes the intracellular pH acidic, favouring H+ excretion and HCO3- recovery

119
Q

Why can having a shabangover cause [HCO3-] to increase?

A

Persistent vomiting

120
Q

What accompanies persistent vomiting?

A

Dehydration

121
Q

What happens when [HCO3-] increases due to persistent vomiting?

A

The kidneys cannot excrete HCO3- as they are trying to compensate for the dehydration. HCO3- and Na+ recovery is favoured to increase the osmolarity of the plasma and cause the osmotic movement of water. In this case, you cannot rely on the kidneys to correct the [HCO3-]

122
Q

What happens if you correct the dehydration by giving fluids after persistent vomiting?

A

HCO3- will be excreted very rapidly

123
Q

Does persistent vomiting cause metabolic acidosis or alkalosis?

124
Q

What is the result of persistent vomiting causing metabolic alkalosis?

A

The body stops actively secreting H+, as it would make the metabolic alkalosis worse

125
Q

What is the result in the decrease of H+ secretion in vomiting induced metabolic alkalosis?

A

As H+ secretion has stopped, so has K+ reabsorption, meaning that a dangerous side effect of persistent vomiting is hypokalaemia

126
Q

Why does a decrease in H+ secretion cause a decrease in K+ reabsorption?

A

Because it stops the antiporter in intercalated cells

127
Q

What does hypokalaemia cause?

A

Paresthesia
Tetany
CVS problems
bad times all round

128
Q

When will metabolic acidosis occur?

A
  • If there is excess metabolic production of acids
  • If acids are ingested
  • If HCO3- is lost
  • If there is a problem with the renal excretion of acid
129
Q

What acids may be metabolically produced?

A
  • Lactic acid

- Ketones

130
Q

What happens if excess acid is produced?

A

The associated anion, e.g. lactate in lactic acid, will replace HCO3- in the plasma

131
Q

What is the result of the associated anion replacing HCO3- in the plasma when excess acid is produced?

A

This will influence the anion gap

132
Q

What is the anion gap?

A

The difference between the sum of the measured concentrations of Na+ and K+ and the sum of the measured concentrations of Cl- and HCO3-

133
Q

When will the anion gap increase?

A

If HCO3- is replaced by another anion, which is not included in the calculation

134
Q

When is the anion gap less likely to change?

A

If the problem causing metabolic acidosis lies within the renal excretion of H+

135
Q

Why will the anion gap be less likely to change if the problem causing the metabolic acidosis lies within the renal excretion of H+?

A

It will change the [HCO3-] directly, without replacement by an unmeasured ion

ESA 3- Urinary System (13 decks)

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