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Gas Exchange and Gas Transport Flashcards

1
Q

Pressures in pulmonary circulation are

A

1/6 of the pressures in systemic circulation

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2
Q

Each gram of Hb combines with how much oxygen?

A

1.34ml O2

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3
Q

Normal Hb
Blood contains how much oxygen per liter

A

150g/L
200ml O2/L

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4
Q

oxygen partial pressure and saturation curve

A
  • partial pressure of O2 against the % saturation of O2
  • sigmoid shape, which flattens at higher levels of O2 saturation
  • increase in partial pressure of O2, increases saturation of O2
  • hypoventilation/hyperventilation or giving oxygen will not make much difference to arterial O2, if above 80mmHg
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5
Q

Oxygen - haemoglobin dissociation curve. bohr effect.

  • affinity affected by?
  • curve shift to the right? Why? Where?
  • curve shift to the left? Why? Where?
A
  • the affinity of Hb for O2 depends on pH, PCO2, 2,3-DPG and temperature
  • metabolising tissues will have high pCO2, low pH, high 2,3-DPG and temperature; curve will shift to the right as causes haemoglobin to dissociate from O2
  • If to the left the affinity to bind increase, if shifting to the right the affinity to dissociate increases.
  • in alveoli curve shifts to the left
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6
Q

What pO2 in arterial blood at atmospheric pressure = SaO2 ?

A

13kPa
97%

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7
Q

P50 (O2-haemoglobin dissociation curve)

A

partial pressure of O2 at which 50% Hb is saturated

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8
Q

below 8kPa O2 is

A

respiratory failure

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9
Q

Hypoxia

A

reduced PaO2 (partial pressure in alveoli)

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10
Q

Hypoxaemia

A

reduced PaO2 (arterial ppO2)

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11
Q

Hypercapnoea

A

high CO2 level in arterial blood

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12
Q

Hypocapnoeae

A

low CO2 level in arterial blood

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13
Q

Respiration definition

A

Gas exchange between the alveoli and pulmonary capillaries by diffusion of O2 and CO2 from an area of high concentration to an area of low concentration down a gradient.

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14
Q

Cellular respiration equation

A

C6H12O6 + 6O2 → 6CO2 + 6 H2O + ATP

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15
Q

CO2 diffusion pathway

A

From an area of high concentration in the pulmonary capillaries to an area of low concentration into the alveoli and is expired.

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16
Q

Is oxygen soluble in plasma?

A

No

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17
Q

How much oxygen at sea level?

A

21kPa

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18
Q

Why does the pressure of oxygen in air higher than in the arteries/mitochondria?

A
  • Oxygen cascade
  • because O2 must diffuse across membranes/compartments to reach mitochondria in cells to take part in cellular metabolism
  • equilibration of gases between alveoli and blood occurs very fast
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19
Q

What is 2,3-DPG a product of?

A

glycolysis

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20
Q

Increased 2,3-DPG causes shift of the oxygen-haemoglobin dissociation curve to the

A

right (dissociation)

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21
Q

Increased pH causes shift of the oxygen-haemoglobin dissociation curve to the

A

right (dissociation)

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22
Q

Decreased temperature causes shift of the oxygen-haemoglobin dissociation curve to the

A

left (higher affinity)

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23
Q

Decreased PCO2 causes shift of the oxygen-haemoglobin curve to the

A

left (higher affinity)

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24
Q

oxygen-haemoglobin dissociation curve and the Bohr effect diagram

A
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25
Q

Cascade of O2 pressures: order of compartments through which O2 must pass to reach the mitochondria.

A

From air → conducting airways → alveoli → interstitial space containing fluid → across the interstitium → red blood cell → bind to Hb → tissue fluid → across cell membrane → mitochondria

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26
Q

cascade of oxygen pressures diagram

A
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27
Q

Fraction of Inspired Oxygen in air is

A

0.21

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28
Q

PIO2 is

A

the partial pressure of O2 in inspired air

20kPa

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29
Q

PIO2 equation

A

FIO2 x Patm
0.21x101 = 20kPa

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30
Q

Why doesn’t upper conducting airways participate in gas exchange?

A

Air is humidified

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31
Q

Apart from O2 content decreasing across each membrane/compartment what decreases the partial pressure of O2?

A

Water vapour we breathe in

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32
Q

What is normal Oxygen saturation: SaO2:

33
Q

The higher the altitude, the

A

lower the atmospheric pressure, the lower the FIO2 and hence the lower the PIO2

34
Q

Alveolar gas equation is used to calculate the

A

partial pressure of O2 in the alveolus

35
Q

What is the alveolar gas equation

A

PAO2= FIO2 (Patm-Ph20)-(PaCO2/R)

R=respiratory quotient=0.8

partial pressure in alveolus =

((FIO2)(atmospheric pressure - pressure of water vapour)) - (partial pressure of CO2/respiratory quotient)

36
Q

What does oxygen delivery (DO2) depend on (2):

A
  • cardiac output (CO)
  • arterial oxygen content (CaO2)
37
Q

What is the equation for cardiac output?

A

heart rate x stroke volume

38
Q

What is the equation for oxygen delivery (DO2)?

A

DO2=COxCaO2

delivery of oxygen = cardiac output x arterial oxygen content

39
Q

What is VO2?

A
  • Oxygen consumption
  • amount of O2 consumed per minute
40
Q

What is VO2 max ( max oxygen consumed per minute) equation?

A

VO2 max = COx(CaO2-CvO2)

oxygen consumption max = cardiac output x (arterial oxygen content - oxygen consumed per minute)

41
Q

What is resting VO2?

A

250ml/minutee

42
Q

At rest in a healthy person, DO2<VO2?

True or False?

A

False
Delivery of oxygen should not be lower than oxygen consumed

43
Q

How many times more soluble is CO2 in plasma than O2?

A

20 times more soluble

44
Q

What % of CO2 is carried as carbaminohaemoglobin?

45
Q

What % of CO2 is carried dissolved in the plasma?

46
Q

What % of CO2 is transported as bicarbonate ions?

47
Q

CO2 dissolving water equation

A

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3 –
Catalysed by enzyme carbonic anhydrase

48
Q

What is the chloride shift?

A
  • RBC membrane is impermeable in hydrogen ions
  • Cl- diffuse into the RBC to maintain electrical neutrality
  • Negatively charged hydrogencarbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane, H+ remains in RBC.
  • To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein
  • If this did not occur then red blood cells would become positively charged as a result of a buildup of hydrogen ions formed from the dissociation of carbonic acid
49
Q

The Haldane Effect

A
  • when haemoglobin becomes deoxygenated in tissues it can take up more CO2
  • In alveoli, oxygenation of Hb results on release of CO2
  • when PO2 rises, the Hb releases CO2 (in lung). When PO2 falls, the Hb binds to CO2 in tissues
50
Q

haldane effect graph

A

Oxygen ability to influence the binding of Hb to CO2 and hydrogen ions
When PO2 rises, the Hb release co2 in lungs, when po2 falls, hb binds to co2 in the tissues

51
Q

Respiratory acidosis

A
  • pH of arterial blood is 7.4 with a H+ concentration of 40nmol/L
  • essential to maintain pH
  • transport of CO” in plasma is critical
  • Bicarbonate and deoxygenated haemoglobin are important buffers which bind and release CO2 according to the pH
  • occurs in type 2 respiratory failure
  • only when high CO2 levels causes low pH
52
Q

How many times more acid equivalent expired daily as CO2 than the amount of acid excreted by the kidneys?

53
Q

Ventilation can be estimated by the

A

rate of CO2 production

54
Q

Respiratory Quotient

A
  • respiratory gas exchange ratio
  • this is the ratio of CO2 production to O2 consumption
  • metabolising carbohydrates produces a volume of CO2 equal to the volume of O2 used, hence ratio is 1.
  • average mixed diet with fats and proteins produces a smaller volume of CO2 than O2 consumed, hence R=0.8
55
Q

Ventilation can be affected by

A

pH, O2, CO2 levels

56
Q

Gas Exchange diagram

A

Blue cells represent venous blood

Purple cells are in the process of becoming oxygenated in the lung

Red cells leaving the alveolar capillary are oxygen rich

57
Q

Acinus

A
  • a unit of respiratory function distal ot the terminal bronchioles comprising of the respiratory bronchioles, alveolar ducts and alveoli
  • many acinar together = pulmonary lobe
  • pulmonary lobules are separated by septae
  • structural independence prevents collapse of an individual unit
58
Q

Alveoli:
- shape, diameter
- lining

A
  • irregular polyhedron, 0.1-0.2 micrometer diameter
  • alveoli are lined by a thin layer by unciliated squamous epithelial cells
59
Q

Type 1 pneumocytes rest on

A

The basement membrane and interface closely with the capillary membrane = alveolar-capillary unit

60
Q

What does the interstitial space between alveoli and capillaries contain?

A

Pulmonary capillaries, elastin and collagen fibers

61
Q

Alveolar - capillary unit membrane size

A

<0.4 micrometers

62
Q

Type 2 pneumocytes

A

found at the junction between alveoli and produce surfactant, which reduced surface tension

63
Q

Club cells (bronchiolar exocrine cells)

A

in alveolar fluid produce glycoaminoglycans

64
Q

No. alveoli always the same in all healthy adults.

True or False?

A

False
Depends on height of individual

65
Q

Size of alveoli depends on the

A

volume of air in the lungs

66
Q

What is the interstitium?

A
  • microscopic space between the alveoli and pulmonary capillaries, 0.5 micrometer
67
Q

interstitium diagram

68
Q

Factors affecting diffusion of gas across alveolar membrane and which laws? Which factors are not relevant to disease? (4)(2)

A
  • thickness of membrane
  • surface area of membrane
  • solubility of gas in the membrane
  • molecular weight of gas
  • Fick’s and Graham’s laws
  • the last two
69
Q

Why does CO2 diffuse more rapidly than O2?

A
  • CO2 has a molecular weight that is 1.4x that of O2
  • but CO2 is 20x more soluble than O2
70
Q

Diffusing Capacity/Transfer Capacity

A
  • the movement of O2 across the alveolar-capillary membrane can be estimated using a small amount of CO (which binds more strongly to Hb)
  • the amount of CO transferred per minute using a single breath method
  • called TLCO/DLCO
71
Q

TLCO be reduced in conditions that affect:

A
  • the surface area available for gas exchange = emphysema
  • thickening of the membrane = pulmonary fibrosis
72
Q

Carboxyhaemoglobin

A
  • CO is colourless, odourless and tasteless
  • formed when carbon monoxide binds to Hb
  • haemoglobin’s affinity for CO is 218 times greater than that for O2, which results in CO displacing O2, during competition for binding sites
73
Q

Clinical symptoms for carbon monoxide poisoning and time:

A
  • within an hour
  • headaches
  • dizziness
  • lethargy
  • weakness
  • confusion
  • coma
  • death
74
Q

Management of carbon monoxide poisoning

A

hyperbaric O2

75
Q

Why can oxygen saturation (SaO2) be falsely normal in patients with carbon monoxide poisoning?

A

CO-Hb is read as Oxy-Hb by finger probes

76
Q

Methaemoglobin

A
  • MetHb arises when the iron component in haemoglobin is oxidises so that it is in the Ferric state (Fe3+)
  • MetHb is unable to bind to O2 and therefore can not participate in O2 transport
77
Q

The main causes of pathological increase in MetHb concentration are:

A
  • congenital/idiopathic methaemoglobinaemia
  • infants become cyanosed
  • acquired MetHb
78
Q

Acquired MetHb

A

post exposure to chemicals (anaesthetics, nitrobenzene and specific antibiotics like dapsone & chloroquine or nitrites)

79
Q

Management of MetHb

A

O2 therapy and methylene blue

HLB (49 decks)

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