Control of Acid/Base Flashcards
1
Q
What is the normal range of plasma pH?
A
7.38-7.46
2
Q
What is the normal H+ concentration of the plasma?
A
37-43nmol/L
3
Q
When are the effects of acidaemia severe?
A
Below pH 7.1
4
Q
When are the effects of acidaemia life threatening?
A
Below pH 7.0
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
6
Q
What is the effect of alkalaemia on calcium salts?
A
Reduces their solubility
7
Q
What is the result of the reduced solubility of calcium salts in alkalaemia?
A
Means that free Ca2+ leaves the ECF
8
Q
How does free Ca2+ leave the ECF?
A
Binds to bone and protein
9
Q
What is the result of free Ca2+ leaving the ECF in alkalaemia?
A
Results in hypocalcaemia
10
Q
What is the effect of hypocalcaemia?
A
Increases the excitability of nerves
11
Q
What happens at pH > 7.45?
A
Parasthesia
Tetany
12
Q
What is tetany?
A
Uncontrolled muscle contractions
13
Q
What happens at pH > 7.55?
A
45% mortality
14
Q
What happens at pH > 7.65?
A
80% mortality
15
Q
Describe the H+ ion concentration of the ECF?
A
It is very low
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
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
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
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-]
20
Q
What is the pCO2 of plasma controlled by?
A
Lungs
21
Q
What is HCO3- created by?
A
Largely RBC
22
Q
What is the concentration of plasma HCO3- controlled by?
A
Kidneys
23
Q
What is the normal [HCO3-]:pCO2 ratio?
A
20:1
24
Q
What is the result of anything that alters the [HCO3-]:pCO2 ratio?
A
It also alters the pH
25
What happens in respiratory alkalaemia?
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
26
What pH is considered respiratory alkalaemia?
>7.45
27
Why must is be respiratory alkalaemia if breathing quickly?
If lungs were fine, breathing would be slowed to raise pCO2
28
What happens in respiratory acidaemia?
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
29
What pH is considered respiratory acidaemia?
<7.35
30
Why must it be respiratory acidaemia if breathing slowly?
Because if lungs were fine, breathing would be sped up to lower pCO2
31
What can compensate respiratory alkalosis or acidosis?
Changes in [HCO3-] controlled by the kidney
32
Why can respiratory acidosis or alkalosis be compensated for by the kidney?
Because the pH is controlled by the ratio, and not absolute values.
33
How does the kidney control [HCO3-]?
Variable renal excretion/production
34
What does the kidney do if pCO2 rises?
[HCO3-] rises proportionally to restore pH
35
What does a rise in [HCO3-] caused by the kidney compensate for?
Respiratory acidosis
36
What does the kidney do if pCO2 falls?
[HCO3-] falls proportionally to restore pH
37
What does a fall in [HCO3-] caused by the kidney compensate for?
Respiratory alkalosis
38
What metabolic processes produce H+ ions?
Metabolism of amino acids or the production of ketones
39
What happens to metabolically produced H+ ions?
They react with HCO3- to produce CO2 in venous blood
40
What happens to the CO2 produced by the reaction of metabolically produced H+ ions?
It is breathed out through the lungs
41
What is the result of the breathing out of the CO2 production by the reaction of metabolically produced H+ ions?
It gives a directly proportional (1mmol acid:1mmol HCO3-) reduction in arterial HCO3-
42
What is the result of the directly proportional reduction in arterial HCO3- caused by metabolically produced H+?
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
43
What is it called when metabolically produced H+ ions cause a pH decrease?
Metabolic acidosis
44
What pH is considered metabolic acidosis?
<7.35
45
What can compensate for metabolic acidosis or alkalosis?
The lungs
46
Why can the lungs compensate for metabolic acidosis or alkalosis?
As pH depends on the ratio of [HCO3-]:pCO2, so the lungs can change pCO2.
47
What do the lungs normally do regarding CO2?
Keep it within tight limits
48
How is CO2 normally kept within tight limits by the lungs?
By central chemoreceptors
49
How do changes in plasma pH drive changes in pCO@?
Via the peripheral chemoreceptors
50
What happens if [HCO3-] falls?
pCO2 is lowered proportionally by increasing ventilation
51
What does the increase in ventilation due to a fall in [HCO3-] compensate for?
Metabolic acidosis
52
What happens if [HCO3-] rises?
pCO2 may be slightly raised by reducing ventilation
53
What does the reduction in ventilation due to a increase in [HCO3-] compensate for?
Metabolic alkalosis, although only partially
54
What happens to pH in respiratory acidosis?
Decreased
55
What happens to pCO2 in respiratory acidosis?
Increased
56
Why is pCO2 increased in respiratory acidosis?
Hypoventilation
57
What happens to [HCO3-] in respiratory acidosis?
Unchanged
58
What happens to pO² in respiratory acidosis?
Decreased
59
What happens to pH in compensated respiratory acidosis?
pH decreased or normal
60
What happens to pCO2 in compensated respiratory acidosis?
Increased
61
What happens to [HCO3-] in compensated respiratory acidosis?
Increased
62
What happens to pO2 in compensated respiratory acidosis?
Decreased
63
What is happening in compensated respiratory acidosis?
Kidneys have increased [HCO3-]. This causes increases in buffering of H+ ions caused by increased pCO2.
64
What happens to pH in respiratory alkalosis?
Increase
65
What happens to pCO2 in respiratory alkalosis?
Decrease
66
Why does pCO2 decrease in respiratory alkalosis?
Hyperventilation
67
What happens to [HCO3-] in respiratory alkalosis?
Unchanged
68
What happens to pO2 in respiratory alkalosis?
Normal or increased
69
What happens to pH in compensated respiratory alkalosis?
Increased or normal
70
What happens to pCO2 in compensated respiratory alkalosis?
Reduced
71
What happens to [HCO3-] in compensated respiratory alkalosis?
Decreased
72
What happens to pO2 in compensated respiratory alkalosis?
Increased
73
What is happening in compensated respiratory alkalosis?
Kidneys have decreased [HCO3-], decreasing buffering of H+ ions
74
What happens to pH in metabolic acidosis?
Decreased
75
What happens to pCO2 in metabolic acidosis?
Unchanged
76
What happens to [HCO3-] in metabolic acidosis?
Decreased
77
What happens to pO2 in metabolic acidosis?
Unchanged
78
What happens to the anion gap in metabolic acidosis?
Increased
79
What is happening in metabolic acidosis?
Decreased [HCO3-] means less buffering of H+ ions
80
Why is here an increase in the amnion gap in metabolic acidosis?
Increase in unmeasured anions because anions associated with increase in H+ has taken HCO3- places
81
What happens to pH in compensated metabolic acidosis?
Decreased or normal
82
What happens to pCO2 in compensated metabolic acidosis?
Decreased
83
What happens to [HCO3-] in compensated metabolic acidosis?
Decreased
84
What happens to pO2 in compensated metabolic acidosis?
Increased or unchanged
85
What happens to the anion gap in compensated metabolic acidosis?
Increased
86
What is happening in compensated metabolic acidosis?
Increased respiratory rate is leading to hypocapnia and therefore raised pH
87
What happens to the pH in metabolic alkalosis?
Increased
88
What happens to pCO2 in metabolic alkalosis?
Unchanged
89
What happens to [HCO3-] in metabolic alkalosis?
Increased
90
What happens to pO2 in metabolic alkalosis?
Unchanged
91
What is happening in metabolic alkalosis?
Increased [HCO3-] means increased buffering of H+
92
What happens to pH in compensated metabolic alkalosis?
It increases or is normal
93
What happens to pCO2 in compensated metabolic alkalosis?
Increase
94
What happens to [HCO3-] in compensated metabolic alkalosis?
Increased
95
What happens to pO2 in compensated metabolic alkalosis?
Decreased or unchanged
96
What is happening in compensated metabolic alkalosis?
Decreased respiratory rate, so hypercapnia, so decreased pH
97
How is HCO3- reabsorbed in the PCT?
- 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
What % of filtered HCO3- is reabsorbed in the PCT?
80-90%
99
Other than the PCT, where else is HCO3- reabsorbed?
In the TAL of the loop of Henle
100
What % of filtered HCO3- is reabsorbed in the loop of Henle?
Up to 15%
101
How does the mechanism of HCO3- reabsorption in the loop of Henle compare to that in the PCT?
It is similar
102
What has happened to HCO3- by the DCT?
Most/all of the filtered HCO3- has been recovered
103
Is the Na+ gradient sufficient to drive H+ secretion in the DCT?
No
104
What is the result of the Na+ gradient being insufficient to drive H+ reabsorption in the DCT?
H+ is pumped across the apical membrane by H+-ATPase
105
What are the H+-ATPase pumps found in the DCT similar to?
Those found in the stomach
106
What happens, regarding K+, when tubular cells export H+?
K+ is absorbed into the blood
107
What is the result of K+ be absorbed into the blood when tubular cells export H+ in tubule lumen?
If you export a lot of H+, you will also absorb a lot of K+
108
What is the result of the relationship between H+ exportation and K+ absorption?
Blood pH is linked to [K+]
109
What is the minimum pH of urine?
4.5
110
Is HCO3- found in urine?
No
111
What is the result of HCO3- not being found in urine?
H+ is buffered by phosphate
112
What kind of acid is phosphate?
Titratable
113
What is meant by phosphate being a titratable acid?
It can freely gain H+ ions in an acid/base reaction
114
What happens to the H+ in urine not buffered by phosphate?
It is attached to ammonia as ammonium
115
What is metabolic acidosis associated with?
Hyperkalaemia
116
Why is metabolic acidosis associated with hyperkalaemia?
As [K+] rises, the kidneys ability to reabsorb and create [HCO3-] is reduced. Hyperkalamia makes the intracellular pH alkaline, favouring HCO3- excretion
117
What is metabolic alkalosis associated with?
Hypokalaemia
118
Why is metabolic alkalosis associated with hypokalaemia?
Because it makes the intracellular pH acidic, favouring H+ excretion and HCO3- recovery
119
Why can having a shabangover cause [HCO3-] to increase?
Persistent vomiting
120
What accompanies persistent vomiting?
Dehydration
121
What happens when [HCO3-] increases due to persistent vomiting?
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
What happens if you correct the dehydration by giving fluids after persistent vomiting?
HCO3- will be excreted very rapidly
123
Does persistent vomiting cause metabolic acidosis or alkalosis?
Alkalosis
124
What is the result of persistent vomiting causing metabolic alkalosis?
The body stops actively secreting H+, as it would make the metabolic alkalosis worse
125
What is the result in the decrease of H+ secretion in vomiting induced metabolic alkalosis?
As H+ secretion has stopped, so has K+ reabsorption, meaning that a dangerous side effect of persistent vomiting is hypokalaemia
126
Why does a decrease in H+ secretion cause a decrease in K+ reabsorption?
Because it stops the antiporter in intercalated cells
127
What does hypokalaemia cause?
Paresthesia
Tetany
CVS problems
bad times all round
128
When will metabolic acidosis occur?
- 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
What acids may be metabolically produced?
- Lactic acid
| - Ketones
130
What happens if excess acid is produced?
The associated anion, e.g. lactate in lactic acid, will replace HCO3- in the plasma
131
What is the result of the associated anion replacing HCO3- in the plasma when excess acid is produced?
This will influence the anion gap
132
What is the anion gap?
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
When will the anion gap increase?
If HCO3- is replaced by another anion, which is not included in the calculation
134
When is the anion gap less likely to change?
If the problem causing metabolic acidosis lies within the renal excretion of H+
135
Why will the anion gap be less likely to change if the problem causing the metabolic acidosis lies within the renal excretion of H+?
It will change the [HCO3-] directly, without replacement by an unmeasured ion
