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Urinary > Acid Base Balance 1&2 > Flashcards

Acid Base Balance 1&2 Flashcards

1
Q

What is the normal pH of arterialised blood?

A

7.4

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2
Q

What is the concentration of free hydrogen ions in blood that has a pH of 7.4?

A

40x10^ -6 mmoles/l

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3
Q

Do bound hydrogen ions contribute to the pH?

A

No - only free ions contribute to the pH

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4
Q

What are the sources of hydrogen ions in the body?

A

Respiratory acid: not normally a factor unless lung function is impaired
Inorganic acids e.g. S-containing amino acids
Organic acids: fatty acids and lactic acid

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5
Q

What is the net gain of hydrogen ions in the body per day?

A

50-100

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6
Q

What is the major source of alkalis in the body?

A

Oxidation of organic anions e.g. citrate

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7
Q

What is the normal bicarbonate level in the body?

A

24 mmoles/l (22-26)

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8
Q

What is the normal CO2 level in the blood?

A

1.2 mmoles/l

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9
Q

What is the normal range of pH in the blood?

A

7.37-7.43

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10
Q

What is the normal value of pCO2?

A

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

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11
Q

How does a buffer system work?

A

It minimises changes in the pH when hydrogen ions are added or removed

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12
Q

What is the ratio of bicarbonate to CO2 when the pH is 7.4?

A

20:1

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13
Q

How does the bicarbonate buffer system decreases the hydrogen ion concentration?

A

The excess hydrogen ions drive the equation to the right so that some of the hydrogen ions are removed from solution

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14
Q

What effect does the buffer system have on CO2 and ventilation?

A

It increases ventilation and decreases CO2

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15
Q

Are the extra hydrogen ions removed from the body?

A

No - the bicarbonate has buffered the hydrogen ions and prevented them contributing to the pH

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16
Q

How are hydrogen ion removed from the body?

A

They are excreted by the kidneys

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17
Q

Which organ controls the bicarbonate concentration?

A

Kidneys

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18
Q

What other buffer exist in the ECF?

A

Plasma proteins and dibasic phosphate

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19
Q

What are the primary intracellular buffers?

A

Proteins, organic/inorganic phosphates and haemoglobin (in erythrocytes)

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20
Q

What is the effect of buffering the hydrogen ions using the ICF buffers?

A

It causes changes in plasma electrolytes since to maintain electrical neutrality movement of hydrogen ions must be accompanied by chloride ions or exchanged for potassium

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21
Q

What is the consequence of moving potassium out of cells into the plasma?

A

Hyperkalaemia: depolarisation of excitable tissues leading to VF and death

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22
Q

Why is there wasting of bones in chronic renal failure?

A

Bone carbonate provides an additional store of buffer

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23
Q

How do the kidneys regulate bicarbonate levels?

A

Reabsorbing filtered bicarbonate and generating new bicarbonate

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24
Q

How is bicarbonate reabsorbed?

A

1) Active hydrogen ion secretion from the tubule cells
2) Couple to passive sodium reabsorption
3) Filtered bicarbonate reacts with the hydrogen to form HC2CO3 which is converted to CO2 and H2O in the presence of carbonic anhydrase
4) CO2 is freely permeable and enters the cell
5) CO2 is converted back to H2CO3 which dissociates to form hydrogen and bicarbonate
6) The hydrogen is then secreted

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25
Q

Where does the majority of bicarbonate reabsorption occur?

A

Proximal tubule

26
Q

Are any hydrogen ions excreted during bicarbonate reabsorption?

A

No

27
Q

What are the minimum and maximum urine pH values?

A

Min: 4.55.0
Max: 8.0

28
Q

Which weak acids and bases act as buffers in the urine?

A

Dibasic phosphate, HPO4, uric acid and creatinine

29
Q

How does Na2HPO4 work in the lumen of the distal tubule?

A

One sodium ion is reabsorbedin exchange for secreted hydrogen. The monobasic phosphate removes the hydrogen from the body

30
Q

Are ammonia or ammonium lipid soluble?

A

Ammonia is

Ammonium is not

31
Q

How is ammonia produced?

A

Deamination of amino acids, mainly glutamine

32
Q

How does ammonia reduce the hydrogen ion concentration?

A

It combines with the secreted hydrogen ions to form ammonium which combines with chloride ions to form NH4CL which is secreted

33
Q

What happens to renal glutaminase activity when the pH falls?

A

Renal glutaminase activity increases and more ammonium is produced and excreted

34
Q

How long does it take the kidney to maximally respond to acid loads?

A

4-5 days because of the requirements of increased protein synthesis

35
Q

What is the max increase in hydrogen ion loss per day in severe acidosis?

A

250mmoles/l

36
Q

What is a drop in pH called?

A

Acidosis

37
Q

What is a rise in pH called?

A

Alkalosis

38
Q

What is respiratory acidosis?

A

pH has fallen due to a respiratory change which has increased pCO2. Results from reduced ventilation and therefore retention of CO2

39
Q

What are the acute causes of respiratory acidosis?

A

Drugs which depress the medullary respiratory centres e.g. barbiturates and opiates
Obstruction of major airways

40
Q

What are the chronic cause of respiratory acidosis?

A

Lung disease e.g. bronchitis, emphysema and asthma

41
Q

What effect will increases pCO2 cause?

A

Increased secretion of hydrogen ions and increase bicarbonate. NH3 production will also start but it takes time

42
Q

How effective is the renal compensation in respiratory acidosis?

A

It will protect the pH but it wall not correct the original disturbance

43
Q

What happens to the blood gas values in chronic respiratory acidosis?

A

They are never normalised

44
Q

What is respiratory alkalosis?

A

An increase in pH due to a fall in pCO2 - increased ventilation and blowing off CO2

45
Q

What are the acute causes of respiratory alkalosis?

A

Voluntary hyperventilation, aspirin and first ascent to altitude

46
Q

What is the chronic cause of respiratory alkalosis?

A

Long term residence at altitude

47
Q

How do the kidneys respond to respiratory alkalosis?

A

Less bicarbonate is reabsorbed to more bicarbonate is lost in the urine

48
Q

What is metabolic acidosis?

A

An acidosis due to a decrease in bicarbonate conc. either due to increased buffering of hydrogen or direct loss of bicarbonate

49
Q

What are the causes of metabolic acidosis?

A

Increased hydrogen production e.g. in diabetic ketoacidosis or in lactic acidosis, failure to excrete the normal dietary load of hydrogen as in renal failure or loss of bicarbonate e.g. as in diarrhoea

50
Q

What happens to ventilation in metabolic acidosis?

A

Ventilation increases in depth rather than rate = Kussmaul breathing

51
Q

How do the kidneys correct metabolic acidosis?

A

By restoring bicarbonate conc. and excreting hydrogen ions

52
Q

What effect does respiratory compensation have in the renal correction of metabolic acidosis?

A

It delays the renal correction but protects the pH (much more important)

53
Q

What happens in metabolic alkalosis?

A

Bicarbonate levels increase and pCO2 will also have to increase

54
Q

What are the causes of metabolic alkalosis?

A

Vomiting: loss of hydrogen ions
Increased renal loss: aldosterone excess/excess liquorice ingestion
Excess administration of bicarbonate
Massive blood transfusions (citrate is used to prevent coagulation but converts to bicarbonate)

55
Q

What happens to the excess bicarbonate in metabolic alkalosis?

A

It is excreted in the urine

56
Q

What effect does high acidity have on potassium levels?

A

It causes hyperkalaemia as the hydrogen ions are buffered intracellularly in exchange for potassium

57
Q

How is the hyperkalaemia treated?

A

1) Give insulin (+ glucose if non-diabetic)
2) Calcium resonium (exchanges calcium ions for potassium ions)
3) Calcium gluconate (IV) - reduces the excitability of the heart and stabilizes the cardiac muscle cell membrane

58
Q

What takes precedence, restoration of volume or correction of metabolic alkalosis?

A

Restoration of volume

59
Q

What is the anion gap?

A

The difference between the sum of the principal cations and the principal anions (usually 14-18mmoles/l)

60
Q

What happens to the anion gap in acidosis due to a loss in bicarbonate?

A

There would be no change

61
Q

What happens to the anion gap in lactic acidosis or diabetic ketoacidosis?

A

The anion gap is increased

Urinary (9 decks)

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