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REN > Acid Base Regulation > Flashcards

Acid Base Regulation Flashcards

1
Q

What is the equation for pH?

A

ph = -log10 [H+]

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2
Q

Give the equation for HCO3- mediated buffering in the circulation.

Which molecule is the base and which is the acid here?

A

H+ + HCO3- = H2CO3 = H2O + CO2

H2CO3 is the acid and HCO3- is the base.

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3
Q

What is the pH of arterial blood?

A

7.4

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4
Q

What is the pH of venous blood?

A

7.35

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5
Q

What is the concentration of HCO3- in arterial blood?

A

24mM

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6
Q

What is the concentration of HCO3- in venous blood?

A

25mM

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7
Q

What is the PCO2 in arterial blood?

A

40 mmHg

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8
Q

What is the PCO2 in venous blood?

A

46mmHg

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9
Q

What is the Henderson-Hasselbalch equation?

A

pH = pK + log10 [base]/[acid]

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10
Q

What is pKa?

A

The pH at which half of a substance is ionised.

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11
Q

How is blood H2CO3 concentration measured?

A

By multiplying PCO2 (mmHg) by 0.03.

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12
Q

What is the equation for blood H+ concentration?

A

[H+] α [CO2] / [HCO3-]

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13
Q

List 4 processes that result in a net hydrogen ion production.

A

1 - ATP hydrolysis.

2 - Anaerobic respiration.

3 - Production of ketones.

4 - Ingestion of acids.

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14
Q

In which condition is ketone production high?

A

Diabetes mellitus.

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15
Q

Why is the kidney implicated in pH regulation?

A
  • Because H+ is removed by combination with HCO3-, which produces excretable H2O and CO2.
  • The loss in HCO3- must be restored by the kidney.
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16
Q

What is the maximum rate of renal HCO3- reabsorption?

A

4 mM / min.

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17
Q

At which plasma HCO3- concentration do you expect HCO3- reabsorption to reach its maximum rate?

A

24 - 25mM (the same as the normal blood HCO3- concentration).

18
Q

How is the kidney able to produce HCO3- when the blood concentration of HCO3- is low?

How is H+ buffered in the tubules during HCO3- production?

A
  • When there is not an excess of HCO3- in the tubular lumen (under the maximum filtration rate), the vasa recta may act as a source of CO2.
  • HPO4 2- acts as a buffer for H+ in the tubules.
19
Q

List 2 factors that limit the rate of renal HCO3- reabsorption.

A

1 - H+ concentration in the proximal tubule.

2 - In turn, the concentration of Na+ / H+ exchangers in the proximal tubule.

20
Q

List the two dominant mechanisms for H+ secretion into the tubular lumen.

A

Primary active transport through:

1 - Apical H+ ATPases.

2 - H+ / K+ ATPases.

21
Q

In which cells does H+ secretion occur in the distal tubule?

A

Alpha intercalated cells.

22
Q

Give the equation for H2PO4- mediated buffering in the urine.

A

H2PO4- = HPO4 2- + H+

23
Q

Where and how is ammonia produced in the kidney?

How does this contribute to the production of HCO3-?

A
  • It is produced in the proximal tubule.
  • It is produced as a byproduct of conversion of glutamine to glutamic acid and then to alpha-ketoglutarate.
  • Alpha ketoglutarate is metabolised to form HCO3-.
24
Q

With which molecule is ammonia in equilibrium in the filtrate?

What is the advantage of having this equilibrium?

A
  • NH4+ is in equilibrium with NH3.

- NH4+ acts as another reservoir for H+.

25
Q

How might ammonia production contribute to Na+ absorption in the proximal tubule?

A
  • NH4+ production in the epithelia will lead to increased H+ and NH3 production.
  • H+ exits the cell via the Na+ / H+ exchanger.
  • NH3 freely diffuses across the apical membrane into the filtrate, where it recombines with H+ to form NH4+ (maintaining the concentration gradient).
26
Q

What is the average pH of filtrate at the end of the proximal tubule?

How does this change by the end of the nephron?

A
  • pH is 6.9 at the end of the proximal tubule.

- By the end of the nephron, pH is highly variable but falls to about 4.5.

27
Q

On a mixed Davenport diagram (diagram 4 on the lecture slides), what do the horizontal lines represent and what do upward-sloping lines represent?

A
  • The upward-sloping lines represent changing HCO3- concentrations at different set concentrations of pCO2.
  • The horizontal lines represent changing pCO2 for different set concentrations of HCO3.
28
Q

List 2 causes of respiratory alkalosis.

A

1 - Hyperventilation.

2 - High altitude.

29
Q

How does the kidney respond to respiratory alkalosis?

A
  • With respiratory alkalosis, CO2 concentration decreases, so the equilibrium shifts towards CO2 according to the HCO3- buffering equation (H+ is lost).
  • In order to restore the pH, the kidney reduces production of HCO3- to shift the equilibrium back towards H+ (produces H+).
30
Q

What might you expect to see on a Davenport diagram for respiratory alkalosis?

A
  • The initial loss of pCO2 will follow the horizontal line (pCO2 for a defined [HCO3-]) downwards and to the right (as pH increases).
  • Where horizontal line intersects the upward-sloping line ([HCO3-] for a defined pCO2), the decrease in HCO3- production will follow the upward-sloping line downwards and to the left (as pH decreases again).
31
Q

Give an example of a cause of respiratory acidosis.

A

Hypoventilation.

32
Q

How does the kidney respond to respiratory acidosis?

A
  • With respiratory acidosis, CO2 concentration increases, so the equilibrium shifts towards H+ according to the HCO3- buffering equation (H+ is produced).
  • In order to restore pH, the kidney increases production of HCO3- to shift the equilibrium back towards CO2 (removes H+).
33
Q

What might you expect to see on a Davenport diagram for respiratory acidosis?

A
  • The initial gain of pCO2 will follow the horizontal line (pCO2 for a defined [HCO3-]) upwards and to the left (as pH decreases).
  • Where the horizontal line intersects the upward-sloping line ([HCO3-] for a defined pCO2), the increase in HCO3- production will follow the upward-sloping line upwards and to the right (as pH increases again).
34
Q

List 4 causes of metabolic acidosis.

A

1 - Renal failure.

2 - Lactic acidosis.

3 - Ketoacidosis.

4 - Poisoning (e.g. aspirin).

35
Q

How does the body respond to metabolic acidosis?

A
  • With metabolic acidosis, H+ goes up, which causes HCO3- to go down OR HCO3- goes down, which causes H+ to go up.
  • In order to restore pH, the CNS increases the ventilation to decrease CO2, returning the pH towards normal (kind of like inducing respiratory alkalosis).
36
Q

What might you expect to see on a Davenport diagram for metabolic acidosis?

A
  • The initial loss of HCO3- will follow the upward-sloping line ([HCO3-] for a defined pCO2) downwards and to the left (as pH decreases).
  • Where the upward-sloping line intersects the horizontal line (pCO2 for a defined [HCO3-]), the decrease in pCO2 will follow the horizontal line downwards and to the right (as pH increases again).
37
Q

List 2 causes of metabolic alkalosis.

A

1 - Vomiting.

2 - Contraction alkalosis.

38
Q

How does the body respond to metabolic alkalosis?

A
  • With metabolic alkalosis, H+ goes down, which causes HCO3- to go up OR HCO3- goes up, which causes H+ to go down.
  • In order to restore pH, the CNS decreases the ventilation to increase CO2, returning the pH towards normal (kind of like inducing respiratory acidosis).
39
Q

What might you expect to see on a Davenport diagram for metabolic alkalosis?

A
  • The initial increase of HCO3- will follow the upward-sloping line ([HCO3-] for a defined pCO2) upwards and to the right (as pH increases).
  • Where the upward-sloping line intersects the horizontal line (pCO2 for a defined [HCO3-]), the increase in pCO2 will follow the horizontal line upwards and to the left (as pH decreases again).
40
Q

If a Davenport diagram is divided into 4 equal quadrants, which conditions are represented by each quadrant and why?

A
  • The top left quadrant represents respiratory acidosis as it is the area where pCO2 is high.
  • The bottom right quadrant represents respiratory alkalosis as it is the area where pCO2 is low.
  • The top right quadrant represents metabolic alkalosis as it is the area where [HCO3-] is high.
  • The bottom left quadrant represents metabolic acidosis as it is the area where [HCO3-] is low.
41
Q

What is the anion gap?

What is the average range for the anion gap?

What does an increase in the anion gap suggest?

A
  • The imbalance in measured bodily anions compared to cations, such that there is a relative excess of cations.
  • The average range for the anion gap is 3-11 mmol/L.
  • An increase in the anion gap suggests that there is a high concentration of anions that are not being accounted for.
42
Q

List 7 causes of an increased anion gap.

A

Generally, causes of acidosis increase the anion gap:

1 - Lactate produced during anaerobic metabolism.

2 - Ketones, especially in diabetes or alcohol toxicity.

3 - Sulfates which accumulate during renal failure.

4 - Phosphates which accumulate during renal failure.

5 - Urate, which accumulates during renal failure.

6 - Hippurate, which accumulates during renal failure.

7 - Aspirin overdose.

REN (19 decks)

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