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urinary > Acid base balance > Flashcards

Acid base balance Flashcards

1
Q

What is the normal PH of arterialised blood

A

7.4 (range 7.37-7.43)

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2
Q

What kinds of protons contribute to pH

A

free protons

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3
Q

How is the respiratory acid which is produced regulated

A

When there is increased production, there is increased ventilation to get rid of CO2 to reduce the production of the carbonic acid

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4
Q

What is the function of buffers

A

Mantain the pH when there are H+ ions added or removed

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5
Q

Which buffer system is most important in the body

A

Bicarbonate buffer system

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6
Q

What does the amount of bicarbonate depend on

A

The amount of CO2 dissolved in plasma and the solubility and partial pressure of the CO2

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7
Q

What is the normal partial pressure of CO2

A

40mmHg (range 36-44 mmHg or 5.3kPa (range 4.8-5.9 kPa)

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8
Q

What is normal bicarbonate

A

24mmoles/L (range 22-26)

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9
Q

Why is the bicarbonate buffer system different to others

A

It is an open buffer system so carbon dioxide is blown out which prevents the equation from reversing to the other direction

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10
Q

What has to follow the movement of a proton

A

A anion (negatively charged) e.g chlorine ion or a cation has to go the opposite way to balance the charge

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11
Q

What does bone carbonate provide

A

Additional store of buffer which is important in chronic acid loads e.g renal failure

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12
Q

How is bicarbonate regulated by the kidney

A

it is reabsorbed and new bicarbonate is also produced

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13
Q

Describe the mechanism for reabsorption of bicarbonate

A

Protons are secreted from the tubule cells
This is coupled to passive sodium reabsorption
Filtered bicarbonate then reacts with secreted H+ to form carbonic acid
then in the presence of carbonic anhydrase on the luminal membrane it is broken down into CO2 and H2O
The CO2 is freely permeable and enters the cell
Within the cell the carbon dioxide which just entered the cell dissolves in water and gets changed into carbonic acid in the presence of carbonic anhydrase which dissociates and becomes a proton and bicarbonate
The proton is secreted
The bicarbonate is reabsorbed into the peritubular capillaries with sodium

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14
Q

where is the majority of bicarbonate reabsorbed

A

proximal tubule (90%)

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15
Q

What happens when too much bicarbonate is excreted

A

Acidosis - the PH of the plasma decreases and becomes more acidic

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16
Q

What is the most important base which acts as a buffer

A

dibasic phosphate

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17
Q

What does titratable acidity result in

A

Bicarbonate production and excreted protons so PH increases

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18
Q

Describe titratable acidity

A

Sodium is taken up from the dibasic phosphate and moves into the cell from the lumen in place of a proton moving the other way
The dibasic Phosphate reacts with the proton in the lumen to make monobasic phosphate
CO2 from the blood moves into the cell which in the presence of carbonic anhydrase dissolves in the water and becomes carbonic acid which then dissociates into bicarbonate and a proton
The proton is secreted and added to the dibasic phosphate while the bicarbonate is reabsorbed into the peritubular capillaries

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19
Q

What is the difference between monobasic and dibasic phosphate

A

monobasic has a 1- charge while dibasic has a 2- charge

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20
Q

Why is phosphate so concentrated at the distal tubule

A

un reabsorbed dibasic phosphate is highly concentrated because the loop of Henle removed a large volume of filtrate which concentrated the phosphate

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21
Q

When is ammonium excretion used

A

Acid loads

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22
Q

Why can ammonia leave the cell membrane but ammonium cannot

A

Ammonia is lipid soluble while ammonium is not

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23
Q

Describe the process of ammonium excretion at the distal tubule

A

Glutamine is deaminated (an ammonia is broken off) in the presence of renal glutaminase
The ammonia is lipid soluble so gets secreted out and combines with secreted protons to produce ammonium
The membrane is impermeable to ammonium so it stays in the lumen to be excreted but combines with chlorine first and then gets excreted
The protons secreted are produced again by CO2 from the blood which dissolves in water in the presence of carbonic anhydrase to become carbonic acid which then dissociates into a proton and bicarbonate
The bicarbonate is reabsorbed

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24
Q

What is different about ammonium excretion at the proximal tubule

A

The ammonium is produced in the cell and is coupled to sodium going into the cell and that allows the ammonium to leave the cell and enter the lumen to be excreted with chloride ions

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25
Q

What controls the activity of renal glutanimase

A

pH - decreased pH causes increased activity of the renal glutanimase so that more ammonium and therefore protons are excreted and bicarbonate produced

26
Q

How long does it take for renal glutanimase to reach full functionality once becoming active

A

4-5 days

27
Q

What is acidosis

A

decrease in pH

28
Q

What is alkalosis

A

increase in pH

29
Q

What do respiratory disorders affect in pH control

A

pCO2

30
Q

What do renal disorders affect in pH control

A

concentration of bicarbonate

31
Q

What is respiratory acidosis

A

Reduced ventilation and therefore increased carbon dioxide in the body

32
Q

What are acute causes of respiratory acidosis

A

Drugs which depress the respiratory centres in the medulla such as barbiturates and opiates
Obstruction of major airway

33
Q

What are chronic causes of respiratory acidosis

A

Lung disease - e.g COPD, Asthma

34
Q

What is the response to chronic respiratory acidosis

A

The respiratory pH control so the kidney needs to take over so increased bicarbonate is what is done - the increased CO2 in the body causes an increased secretion of protons and increased production of bicarbonate
The acidic conditions stimulates renal glutanimase for ammonium excretion but again that takes 4-5 days to activate

35
Q

What is respiratory alkalosis

A

Increased ventilation and CO2 blow off so therefore decreased partial pressure of CO2

36
Q

What are the acute causes of respiratory alkalosis

A

Voluntary hyperventilation, aspirin and being at high altitude for a short time

37
Q

What are chronic causes of respiratory alkalosis

A

Long term stay at high altitude - decreases partial pressure of oxygen so the peripheral chemoreceptors are stimulated to increase ventilation

38
Q

How is pH protected in respiratory alkalosis

A

Bicarbonate concentration is reduced - less CO2 so less protons for excretion an therefore less bicarbonate is reabsorbed so it is lost in the urine

39
Q

What is metabolic acidosis

A

Decrease in bicarbonate concentration due to increased proton buffering or direct loss of bicarbonate

40
Q

What are the causes of metabolic acidosis

A

Increased proton production in ketoacidosis of a diabetic or lactic acidosis
Failure to excrete the normal amount of protons which are consumed in a day which occurs in renal failure
Loss of bicarbonate like in conditions such as diarrhoea

41
Q

How is pH regulated in metabolic acidosis

A

Ventilation is stimulated to decrease the carbon dioxide so ventilation increases (in depth more than rate) Kussmaul breathing in renal failure or diabetic ketoacidosis

42
Q

What is kussmaul breathing

A

Established clinical sign of renal failure or diabetic ketoacidosis where the ventilation reaches a max of 30L/min compared to the normal of 5/6 L/min - this occurs when pH reaches 7.0

43
Q

Why is the pH not completely compensated in metabolic acidosis

A

Full compensation would mean that there would be no drive to fix the original disturbance of what is causing the issue so by not correcting fully, there is still the intent to get the primary disturbance fixed

44
Q

What is the immediate response when there is increased metabolic protons within the body

A

Immediate buffering of the ECF and then ICF

45
Q

What is the response which occurs minutes after when there is increased metabolic protons within the body

A

Respiratory compensation

46
Q

What is the response which takes days when there is increased metabolic protons within the body

A

ammoniumexcretion; Renal correction of the disturbance due to the renal glutanimase taking 4-5 days to reach its maximum - as the bicarbonate begins to increase back up, the respiratory compensation begins to decrease

47
Q

How does respiratory compensation delay the renal correction in metabolic acidosis and why is it important

A

The respiratory compensation is important because it protects the pH but it delays the renal correction because it decreases the CO2 partial pressure so there is less CO2 for proton secretion and bicarbonate production which means it takes longer to correct the renal disturbance

48
Q

What is metabolic alkalosis

A

Bicarbonate must have increased - PCO2 will increase to correct it

49
Q

What are the causes of metabolic alkalosis

A

Increased proton loss via vomiting
Increased renal proton loss e.g aldosterone and liquorice excess
Excess administration of bicarbonate in a renal impaired individual
More then 8 units of blood transfusion due to the coagulant citrate which is converted into bicarbonate by the body

50
Q

which hormone is liquorice’s effect like

A

Aldosterone

51
Q

Give the summary of respiratory acidosis (if its protons, PH increased or decreased and what the initial disturbance and compensated were)

A

Increased protons - decreased pH
Initial disturbance was an increase in partial pressure of CO2 and the compensated was increased bicarbonate
(The compensation is always the same direction as the disturbance - increase is fixed by increase)

52
Q

Give the summary of respiratory alkalosis (if its protons, PH increased or decreased and what the initial disturbance and compensated were)

A

Decreased protons - decreased pH
Initial disturbance was an decrease in partial pressure of carbon dioxide which was compensated by decrease in bicarbonate

53
Q

Give the summary of metabolic acidosis (if its protons, PH increased or decreased and what the initial disturbance and compensated were)

A

Increased protons - decreased pH
Initial disturbance was a decrease in bicarbonate which was compensated by decrease partial pressure CO2

54
Q

Give the summary of metabolic alkalosis (if its protons, PH increased or decreased and what the initial disturbance and comprensation were)

A

Decreased protons - increased pH
initial disturbance was an increase in bicarbonate which was compensation by an increased partial pressure CO2

55
Q

Why is there a smaller decrease in chronic respiratory acidosis compared to acute when there is an increase in partial pressure of CO2

A

In chronic, the 4-5 days for the renal glutanimase to be activated is complete so the ammonium excretion system is working fully which has a greater capability to raise bicarbonate then titratable acidity which is what the acute respiratory acidosis will have to use
(similar difference seen in chronic respiratory alkalosis because of delay in turning of ammonium excretion system)

56
Q

What to do when someone has combined metabolic and respiratory acidosis

A

Treat with insulin to uptake more potassium into the cells due to the potassium being high in the plasma as it is exchanged for protons - the hyperkalaemia poses threat of ventricular fibrillation

57
Q

The following blood gas values were seen in a patient. Which simple Acid/Base Disturbance has he got?

pH = 7.32, [HCO-3]= 15 mM, PCO2 = 30mmHg (4kPa)

A

Metabolic acidosis

58
Q

The following blood gas values were seen in a patient. Which simple Acid/Base Disturbance has he got?

pH = 7.32, [HCO-3]= 33 mM, PCO2 = 60mmHg (8kPa)

A

Chronic respiratory acidosis - large change in CO2 and minimal change in pH

59
Q

The following blood gas values were seen in a patient. Which simple Acid/Base Disturbance has he got?

pH = 7.45, [HCO-3] = 42 mM, PCO2 = 50mmHg (6.7kPa)

A

Metabolic alkalosis

60
Q

The following blood gas values were seen in a patient. Which simple Acid/Base Disturbance has he got?

pH = 7.45, [HCO-3]= 21 mM, PCO2 = 30mmHg (4kPa)

A

Respiratory alkalosis - the pH is not well protected and only a small change in bicarbonate which means that the renal glutanimase is not functioning fully yet so it has been less than 4-5 days

61
Q

A 75 year old man has the following blood gas values:
pH = 7.31, PCO2 = 7.7.kPa, (58mmHg), [HCO3-] =36mmoles/l. - what condition has caused these

A

Chronic respiratory condition due to large change in bicarbonate so renal glutanimase must be active

62
Q

The following acid/base values were obtained:
pH = 7.25, [HCO3-] = 12mmoles/l, PCO2 = 3.3kPa (25mmHg)
What condition might have caused this

A

Renal impairment (metabolic acidosis )

urinary (24 decks)

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