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Physiology- CP > Acid-Base Biochemistry > Flashcards

Acid-Base Biochemistry Flashcards

1
Q

What is pH?

A
  • The concentration of hydrogen ions in a solution
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2
Q

What is the expression for pH?

A

pH = -log[H+]

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3
Q

What is the importance of H+ ions?

A
  • Reactive and readily combine with negative charges and proteins
  • Alter conformational shape
  • Disrupt tertiary structure, disrupt active sites, disrupts subsequent function
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4
Q

What is the optimal pH range for most enzymes?

A
  1. 35-7.45 [H+]= 25-45 nmol/L

- Not true for all enzymes, e.f. pepsin and trypsin

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5
Q

When does acidosis occur (in terms of pH)?

A
  • Falls below reference
  • pH= 6.9-7.35
    [H+] = 46-125 nmol/L
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6
Q

When does alkalosis occur (in terms of pH)?

A
  • Rises above reference range
  • pH = 7.45-7.8
  • [H+] = 16-34 nmol
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7
Q

Define an acid

A
  • Compounds which form H+ in solution

- Proton donors

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8
Q

Define a base

A
  • Compounds that bind H+

- Proton acceptors

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9
Q

What is a strong acid/base?

A
  • Dissociates completely in solution
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10
Q

What are weak acids/bases?

A
  • Only partially ionised in solution

- Exists in equilibrium with ions

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11
Q

What is the Henderson-Hasselbalch equation?

A

HA H+ + A-

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12
Q

What is the principle behind the Henderson-Hasselbach equation?

A
  • For any weak acid/base, the pH of the solution is determined by the ratio of dissociated base to undissociated acid
  • pH is dependent on amount of acid and amount of conjugate base as well as the extent to which they dissolve
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13
Q

Describe a buffer

A
  • Weak acid/base
  • Accepts H+ when concentration of acid increases
  • Releases H+ when concentration of acid decreases
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14
Q

What is meant by buffer capacity?

A
  • Buffers are only effective within a certain range of [H+]

- Once capacity is exceeded buffer will no longer be able to maintain pH

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15
Q

How does a buffer affect the Henderson-Hasselbalch equation?

A

HA H+ + A-

  • Adding acid (H+) drives reaction to left
  • Adding alkali removed H+ and drives reaction to the right
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16
Q

What is the bicarbonate buffer?

A

CO₂+H₂O H₂CO₃ H⁺+HCO₃⁻

  • Components can be regulated
  • CO₂ by the lungs and bicarbonate by the kidneys
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17
Q

Describe proteins as buffers

A
  • Most abundant buffers but are not modifiable
  • Carry net negative charge at physiological pH so can absorb H+
  • Haemoglobin has the highest concentration in the blood
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18
Q

Describe phosphate buffer

A

HPO₄²⁻ + H⁺ H₂PO₄

  • Important in urine
  • Concentration too low in blood to be an effective buffer
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19
Q

What is the significance of acid-base balance?

A
  • Maintaining pH within these limits is vital
  • Acid produced by the body is dealt with by a 2-step process
  • H+ buffered by physiological buffers
  • Acid products are eliminated via lungs and kidneys
  • i.e. acid base balance is the process which maintains [H+] within normal limits
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20
Q

What are the sources of acid?

A
  • Acid constantly produced in body
  • Metabolism
  • Ingestion of external acid (aside from overdose) generally has little effect on pH
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21
Q

How is acid excreted?

A
  • Metabolic acid by kidneys

- Carbon dioxide removed through lungs

22
Q

How is sulphuric acid produced in the body?

A
  • From oxidation of sulphur-containing amino acids such as cysteine
23
Q

How is phosphoric acid produced in the body?

A
  • From dietary phosphate
24
Q

How is lactic acid produced in the body?

A
  • From anaerobic respiration
25
Q

How are ketone bodies produced in the body?

A
  • β-hydroxybutyric acid + oxaloacetic acid
  • High in type 1 diabetes
  • Ketoacidosis
26
Q

What enzyme catalyses the reaction producing bicarbonate ions?

A

Carbonic anhdydrase

27
Q

Which organ is more effective at removing acid?

A

Lungs, kidneys are slow

- Average person generates around 13 moles of CO₂ a day

28
Q

How is H+ produced and how is it buffered?

A
  • Produced from respiration

- Buffered by bicarbonate and Hb

29
Q

How does the addition of carbon dioxide affect oxygen delivery?

A
  • Drives it
30
Q

What is respiratory acidosis?

A
  • Increase PaCO₂ and H+ in hypoventilation

- Carbon dioxide is not released which leads to acidity

31
Q

What is respiratory alkalosis?

A
  • Decrease PaCO₂ and H+ hyperventilation
32
Q

What is metabolic acidosis?

A
  • Non-respiratory acidosis, increase in H+ and decrease in bicarbonate
33
Q

What is metabolic alkalosis?

A
  • Non-respiratory decrease in H+ and increase in bicarbonate
34
Q

What do clinical acid base machines measure?

A
  • Arterial blood gas

- Direct PaCO₂, PaO₂ and pH (via an electrode)

35
Q

How is [HCO₃⁻] measured?

A
  • Derived from pH and PaCO₂ using the Henderson-Hasselbalch equation
36
Q

What measurements can be estimated from the bicarbonate concentration?

A
  • Standard bicarbonate

- Base excess

37
Q

What controls ventilation?

A

Carbon dioxide

38
Q

What is the normal range for PaCO₂?

A
  • 4.8 - 6.1kPa
    > 6.1 is respiratory acidosis
    <4.8 is respiratory alkalosis
39
Q

Why is the pH not the most reliable indicator of respiratory acidosis/alkalosis?

A
  • pH may be within normal range as a result of metabolic compensation
  • However, if PaCO₂ is outside normal range, respiratory acidosis/alkalosis still exists
40
Q

How much of carbon dioxide is carried as the bicarbonate ion?

A
  • 80%
  • Each kPa of carbon dioxide will increase bicarbonate by around 1mmol/L
  • Determined by respiratory rate
41
Q

Why is bicarbonate not a very important measurement?

A

Ambiguous

42
Q

What does a proportionate change in PaCO₂ and HCO₃⁻ suggest?

A

Respiratory acid base imbalance

43
Q

What does a disproportionate change in PaCO₂ and HCO₃⁻ suggest?

A

Metabolic acid base imbalance

44
Q

What is the base excess?

A

Change in bicarbonate concentration produced by the metabolic component of an acid-base disturbance
- Deviation away from what normal bicarbonate should be

45
Q

What would the base excess be in metabolic acidosis?

A

Base excess is negative because there is not enough bicarbonate

46
Q

What would the base excess be in metabolic alkalosis?

A

Base excess is positive because there is too much bicarbonate

47
Q

What is the standard bicarbonate?

A
  • It is in estimate of what the HCO₃⁻ would be if PaCO₂ was normal
  • Value removes the respiratory influence on the buffer capacity
    SB= normal bicarbonate +/- base excess HCO₃⁻
48
Q

What is the normal range for the anion gap?

A

10-18 mmol/l

Diagnostic and plasma must be neutral

49
Q

What is the most common cause of increased anion gap (with examples)?

A
  • Metabolic acidosis, e.g.
  • Drug toxicity- salicylates (Acetosalicylate)
  • Alcohol- methanol generated formate
  • Diabetic ketoacidosis (acetoacetate)
50
Q

What type of metabolic acidosis does not increase anion gap?

A
  • Tubular acidosis

- Increases Cl- accompanies the HCO₃⁻ loss anion gap is retained

51
Q

Why is a normal HCO₃⁻ not necessarily indicative of no acid base disorder?

A
  • In a double (respiratory + metabolic) acidosis, respiratory acidosis increases bicarbonate while metabolic acidosis will decrease
  • Two effects then cancel out
  • But base excess will still be difference

Physiology- CP (19 decks)

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