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Chemical Pathology Wits > Acid Base Balance > Flashcards

Acid Base Balance Flashcards

1
Q

Define external respiration

A

Exchange of O2 and CO2 in the lungs between alveolar air and pulmonary blood

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2
Q

To which ventricle does oxygenated pulmonary blood return?

A

Left ventricle

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3
Q

What governs the diffusion of O2 and CO2 across alveolar and cell membranes?

A

Gradients in the partial pressure of each gas
- high partial pressure to low partial pressure
- the greater the difference, the faster the diffusion

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4
Q

What is the barometric pressure of air at sea level?

A

101kPa

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5
Q

How much O2 and CO2 does inspired air contain?

A

21% O2
0.03% CO2

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6
Q

What is the pO2 in inspired air?

A

21kPa

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7
Q

What is the pO2 in alveolar air?

A

13.3kPa

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8
Q

What is the pO2 in pulmonary capillaries?

A

5.3kPa

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9
Q

What is the pO2 in arterial blood?

A

11.9kPa

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10
Q

What is the pO2 in venous blood?

A

5.3kPa

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11
Q

What is the pO2 in expired air?

A

15.3kPa

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12
Q

What is the pCO2 in inspired air?

A

0.03kPa

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13
Q

What is the pCO2 in alveolar air?

A

5.3kPa

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14
Q

What is the pCO2 in pulmonary capillaries?

A

6.1kPa

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15
Q

What is the pCO2 in arterial blood?

A

5.3kPa

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16
Q

What is the pCO2 in venous blood?

A

6.1kPa

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17
Q

What is the pCO2 in expired air?

A

4.0kPa

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18
Q

Is CO2 more or less water soluble than O2

A

22x more soluble than O2

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19
Q

How does CO2 water solubility affect diffusion across cell membranes?

A

Diffuses rapidly

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20
Q

How is C2 predominantly transported?

A

In solution as bicarbonate (HCO3-)

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21
Q

How is blood’s oxygen carrying capacity supplemented?

A

O2 is bound to haemoglobin (poorly water soluble)

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22
Q

Discuss haemoglobin

A

2 pairs of identical globin chains
- 2 alpha
- 2 non-alpha
Each globin contains a heme group

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23
Q

What is heme?

A

A porphyrin ring containing Fe2+ in the centre (site of O2 binding and release)

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24
Q

Discuss oxygen binding to haemoglobin

A
  1. O2 binds to the Fe2+ of the heme group
  2. 4 heme groups means 4 O2 molecules bound
  3. Once bound, haemoglobin undergoes a reversible conformational change which increases its O2 affinity
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25
Q

How is oxygen released from haemoglobin?

A
  1. When blood reaches tissues, pO2 is low and O2 is rapidly released
  2. Conformational changes reverse
26
Q

Which substrate prevents binding of deoxyhaemoglbin to O2?

A

2,3 - DPG

27
Q

What shape is the relationship between pO2 and blood O2 content and what is this curve called?

A

Oxygen dissociation curve
Sigmoidal

28
Q

What can reduce the affinity of haemoglobin for O2?

A
  1. Increase pCO2
  2. Decrease pH
29
Q

What is the “Bohr” effect?

A

Factors that reduce affinity of Hb for O2 cause a downward shift in the oxygen dissociation curve

30
Q

What is adequate gas exchange between the alveolar air and pulmonary blood dependent on?

A
  1. Number of functional alveoli
  2. Diffusion distances between alveoli and blood
  3. Alveolar ventilation
  4. Alveoli perfusion
  5. Matching of alveoli ventilation and perfusion
31
Q

What controls the respiratory rate in the human body and what does it respond to?

A

Medullary respiratory center
Responds to pH changes

32
Q

How does hypoventilation affect pCO2 and pO2?

A

pCO2 - increased
pO2 - decreased

33
Q

How does hyperventilation affect pCO2 and pO2?

A

pCO2 - decreased
pO2 - stays the same

34
Q

Why does pO2 stay the same in hyperventilation?

A

Hb already maximally saturated

35
Q

How does mild increase in diffusion distance affect pCO2 and pO2?

A

pCO2 - stays the same
pO2 - decreased

36
Q

How does severe increase in diffusion distance affect pCO2 and pO2?

A

pCO2 - increased
pO2 - decreased

37
Q

Why does pCO2 not increase with mild increase in diffusion distance?

A

pCO2 is much more diffusible

38
Q

How does mild V/Q mismatch affect pCO2 and pO2?

A

pCO2 - stays the same
pO2 - decreased

39
Q

Why does pCO2 not increase with mild V/Q mismatch?

A

Compensatory hyperventilation of normal alveoli can remove excess CO2

40
Q

How does severe V/Q mismatch affect pCO2 and pO2?

A

pCO2 - increased
pO2 - decreased

41
Q

Which biochemical parameters are used to assess respiratory function?

A

pCO2
pO2
pH

in ARTERIAL blood

42
Q

Why must samples for respiratory function be sealed and not in contact with air?

A
  1. O2 and CO2 exchange
  2. Microbial growth
  3. Evaporation
  4. Chemical reactions
43
Q

What is a normal blood hydrogen ion concentration?

A

35-45nmol/L (3.5-4.5x10*8 mol/L)

44
Q

Who formulated the term pH to describe free hydrogen ion concentration?

A

Sorenson

45
Q

What is the definition of pH?

A

pH = -log [H+]

46
Q

Name the mechanisms of normal metabolism that produce hydrogen ions constantly

A
  1. Complete metabolism of fat and carbohydrates
  2. Oxidative metabolism of proteins, nucleic acids and phospholipids
47
Q

How does aerobic/complete metabolism of carbohydrates and fats produce hydrogen ions?

A

Produces CO2 -> in solution, forms carbonic acid

CO2 + H2O <-> H2CO3 <-> HCO3- + H+

48
Q

How does oxidative metabolism of proteins, nucleic acids and phospholipids produce hydrogen ions?

A

Produces phosphoric acid, sulphuric acid in solution -> dissociate to yield hydrogen ions and specific anion

49
Q

How is CO2 removed from the body?

A

Respiratory expiration

50
Q

How are hydrogen ions removed from the body?

A

Excreted by kidneys

51
Q

How is the strength of an acid defined?

A

Defined by its tendency to dissociate AKA produce free hydrogen ions

Strong acid - dissociates completely even in acidic solutions

Weal acid - dissociates partially, reaching equilibrium between the acid HA and its conjugate base A-

52
Q

Give an example of a strong acid and its chemical formula

A

H2SO4 -> H+ + HSO4-

53
Q

Give an example of a weak acid and its chemical formula

A

H3PO4 <-> H+ + H2PO4-
H2CO3 <-> H+ + HCO3-
NH4+ <-> H+ + NH3

54
Q

What is a buffer?

A

A solution containing a conjugate acid-base pair made of a weak acid and its salt which minimises pH changes

55
Q

How is the strength of an acid measured?

A

By its dissociation constant ‘K’

56
Q

What is the formula for K?

A

K = [H+][A-]/[HA]

57
Q

What is the formula for pK?

A

-log K

58
Q

What is the value for K in a strong versus weak acid?

A

K>1 strong acid
K<10*-3 weak acid

59
Q

What is the value for pK in a strong versus weak acid?

A

pK <0 strong acid
pK >3 weak acid

60
Q

How does excess H+ shift the equilibrium of the buffer reaction?

A

Shifts towards acid

61
Q

How does deficiency H+ shift the equilibrium of the buffer reaction?

A

Shift towards base

62
Q
A

Chemical Pathology Wits (4 decks)

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