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Acid-base balance Flashcards

1
Q

What is normal plasma pH?

A

7.35 - 7.45

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2
Q

What is the relative concentration of hydrogen ions in the plasma with a pH of 7.35 - 7.45?

A

Low concentration of hydrogen ions

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3
Q

What are the three systems involved in controlling plasma pH?

A

Bicarbonate buffer system

Respiratory system

Kidneys

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4
Q

How is the bicarbonate buffer system set up?

A

Dissolved carbon dioxide in red blood cells and in plasma

carbon dioxide + water bicarbonate ion + hydrogen ion

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5
Q

What does the direction of the bicarbonate buffer reaction depend on?

A

The concentrations of reactants and products

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6
Q

How do the concentrations of reactants and products affect the direction of the bicarbonate buffer reaction?

A

Higher concentration of reactants favours forwards direction

Higher concentration of products favours backwards direction

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7
Q

What is the concentration of bicarbonate ions in the plasma?

A

25mmol/L

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8
Q

Why is the concentration of bicarbonate ions in the plasma so high?

A

Because in red blood cells
hydrogen ions bind to haemaglobin, removing them from solution, reducing their concentration
favours forward reaction
more bicarbonate ions produced
more bicarbonate ions transported into plasma

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9
Q

Why do hydrogen ions bind to haemaglobin?

A

Because hydrogen ions are positively charged and haemaglobin is negatively charged

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10
Q

What is the concentration of carbon dioxide in the plasma?

A

1.2mmol/L

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11
Q

How does the higher concentration of bicarbonate ions than carbon dioxide in the plasma affect the bicarbonate buffer reaction?

A

Favours backwards reaction

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12
Q

How does the backwards reaction of the bicarbonate buffer reaction affect plasma pH?

A

Fewer hydrogen ions produced, more hydrogen ions used up

increases plasma pH to slightly alkaline

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13
Q

What controls the concentration of bicarbonate ions in the plasma?

A

The kidneys

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14
Q

How do the kidneys control the concentration of bicarbonate ions in the plasma?

A

Variable reabsorption, production and excretion

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15
Q

What does the concentration of carbon dioxide in the plasma depend on?

A

pCO2 of plasma

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16
Q

What does the pCO2 of plasma depend on?

A

pCO2 of alveoli

Metabolism producing CO2

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17
Q

What does the pCO2 of alveoli depend on?

A

Alveolar ventilation

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18
Q

What is the equation for calculating pH?

A

Henderson Hasselbach equation

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19
Q

What is the Henderson Hasselbach equation for plasma pH?

A

pH = pK + log [HCO3-] / [CO2]

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20
Q

What is the value of pK at 37C?

A

6.1

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21
Q

What is the order in which the systems controlling pH act when there is a change in pH?

A

Bicarbonate buffer system

then respiratory system

then kidneys

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22
Q

What has happened to hydrogen ion concentration when there is a decrease in pH?

A

Increased hydrogen ion concentration

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23
Q

What happens to the direction of the bicarbonate buffer reaction when there is decrease in plasma pH?

A

Favours backwards reaction

24
Q

What happens to the hydrogen and bicarbonate ion concentration and pCO2 in response to a decrease in plasma pH?

A

Hydrogen and bicarbonate ions react, reducing their concentrations

Carbon dioxide is produced, increasing plasma pCO2

25
What happens to the plasma pCO2 after the response to a decrease in plasma pH?
Stimulates central chemoreceptors stimulates increased alveolar ventilation more carbon dioxide expired decreases plasma pCO2
26
What happens to the plasma bicarbonate ion cocnentration after the response to a decrease in plasma pH?
Stimulates kidneys to reabsorb more, produce more, excrete less increases plasma bicarbonate ion concentration
27
What has happened to hydrogen ion concentration when there is an increase in pH?
Decreased hydrogen ion concentration
28
What happens to the direction of the bicarbonate buffer reaction when there is an increase in plasma pH?
Favours forwards reaction
29
What happens to the plasma hydrogen and bicarbonate ion concentration and pCO2 in response to an increase in plasma pH?
Carbon dioxide and water react, decreasing plasma pCO2 Hydrogen and bicarbonate ions produced, increasing their plasma concentration
30
What happens to the reduced plasma pCO2 after the response to an increase in plasma pH?
Stimulates central chemoreceptors reduce alveolar ventilation less carbon dioxide expired increase in plasma pCO2
31
How effective is response to reduced plasma pCO2? Why?
Not very effective reducing alveolar ventilation is limited because this reduces plasma pO2 which then stimulates peripheral chemoreceptors...
32
What happens to the increased plasma bicarbonate ion concentration after the response to an increase in plasma pH?
Kidneys reabsorb less, produce less and excrete more bicarbonate ions reduce their plasma concentration
33
How do the kidneys control plasma pH?
Variable reabsorption, production and excretion of bicarbonate ions Variable secretion of hydrogen ions
34
What part of the nephron does bicarbonate reabsorption occur in?
Proximal convoluted tubule Later distal convoluted tubule Collecting ducts
35
How are bicarbonate ions reabsorbed in the proximal convoluted tubule?
Sodium bicarbonate in the tubular lumen dissociates into sodium ion and bicarbonate ion NHE on apical domain of epithelial cell Moves sodium ions down their concentration gradient from the lumen into the cell, whilst moving hydrogen ions against their concentration from the cell into the lumen, so is secondary active transport Hydrogen ions in the lumen combine with bicarbonate ions in the lumen to form carbonic acid Carbonic anhydrase converts carbonic acid into carbon dioxide and water Carbon dioxide and water move from the lumen into the cell by simple diffusion Carbonic anhydrase converts carbon dioxide and water into carbonic acid Carbonic acid dissociates into bicarbonate ion and hydrogen ion Na-HCO3- co-transporter on basolateral domain of epithelial cell Moves sodium ion and bicarbonate ion from epithelial cell into interstitial fluid
36
What is the difference between bicarbonate ion reabsorption in the late distal convoluted tubule and collecting ducts compared to proximal convoluted tubule?
AE on basolateral domain of epithelial cell | moves bicarbonate ion from cell into interstitial fluid, whilst moving chloride ion from interstitial fluid into cell
37
What part of the nephron does hydrogen ion secretion occur in?
Later distal convoluted tubule Collecting ducts
37
What type of cell in the late distal convoluted tubule and collecting ducts does hydrogen ion secretion occur in?
Intercalated cells | type A
39
How does hydrogen ion secretion occur in the later distal convoluted tubule and collecting ducts?
Carbon dioxide diffuses from interstitial fluid into epithelial cell carbon dioxide + water hydrogen ion + bicarbonate ion H+ K+ ATPase on basolateral domain of epithelial cell actively transports one hydrogen ion from the cell into the lumen whilst actively transporting one potassium ion from the lumen into the cell H+ ATPase on basolateral domain of epithelail cell actively transports one hydrogen ion from the cell into the lumen
40
Why are bicarbonate ions normally reabsorbed whilst hydrogen ions are normally secreted?
Because bicarbonate ions in the plasma are used up by reacting with hydrogen ions from acids produced by metabolism Hydrogen ions from acids produced by metabolism are secreted
41
What are some examples of acids produced by metabolism?
Lactic acid Keto acids
42
How does bicarbonate ion reabsorption and hydrogen ion secretion affect the urine?
Makes it acidic, lower pH
43
What is the minimum pH of urine?
4.5
44
What happens to hydrogen ions in the lumen of the nephron?
Bicarbonate buffer system When this is not present phosphate buffer system ammonia buffer system
45
What is the phosphate buffer system?
HPO4-- + H+ -----> H2PO4-
46
What is the ammonia buffer system?
NH3 + H+ -----> NH4+
47
What part of the nephron does bicarbonate production occur in?
Proximal convoluted tubule Later distal convoluted tubule
48
How are bicarbonate ions produced in the proximal convoluted tubule?
Glutamine -----> a-ketoglutarate + NH3+ + H+ A-ketoglutarate -----> 2HCO3-
49
What happens to the bicarbonate ions produced in the proximal convoluted tubule?
Na-HCO3- transporter on basolateral domain of epithelial cell moves both sodium ion and bicarbonate ion from epithelial cell into interstitial fluid
50
What happens to the ammonium produced by bicarbonate ion production?
Diffuses across apical domain from epithelial cell into tubular lumen NH3 + H+ -----> NH4+ cell membrane is impermeable to NH4+ remains in lumen
51
What type of cell in the later distal convoluted tubule does bicarbonate ion production occur in?
Intercalated cell | type A
52
How are bicarbonate ions produced in the later distal convoluted tubule?
Carbon dioxide + water bicarbonate ion + hydrogen ion | catalysed by carbonic anhydrase
53
What happens to the bicarbonate ions produced in the later distal convoluted tubule?
AE on basolateral domain of epithelial cell | moves bicarbonate ion from cell into interstitial fluid, whilst moving chloride ion from interstitial fluid into cell
54
How does the pH change along the nephron? Why?
Decreases across proximal convoluted tubule | due to bicarbonate ion reabsorption
55
Does the phosphate buffer system or the ammonia buffer system bind more hydrogen ions?
Ammonia buffer system

Respiratory system (32 decks)

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