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Respiratory: Physiology > Gas Exchange > Flashcards

Gas Exchange Flashcards

1
Q

What is anatomical dead space?

A

Some inspired air remains in the airways where it is not available for gas exchange

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2
Q

What is the equation for pulmonary ventilation (PL)?

A

PL = tidal volume (l/breath) x respiratory rate (breath/min)

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3
Q

Calculate pulmonary ventilation when tidal volume = 0.5 l/breath and respiratory rate is 12 breath/min

A

PL = 6 l/min

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4
Q

What are the units for pulmonary ventilation?

A

L/min

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5
Q

Why is alveolar ventilation less than pulmonary ventilation?

A

Due to presence of anatomical dead space

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6
Q

What is the equation for alveolar ventilation?

A

AV = (tidal volume - dead space volume) x respiratory rate

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7
Q

Calculate alveolar ventilation when tidal volume is 0.5, dead space volume is 0.15, and respiratory rate is 12

A

AV = 4.2 l/min

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8
Q

What is pulmonary ventilation?

A

The volume of air breathed in and out per minute

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9
Q

What is alveolar ventilation?

A

The volume of air exchanged between the atmosphere and alveoli per minute

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10
Q

How is pulmonary ventilation increased (e.g. during exercise)?

A

Increasing both the depth (tidal volume) and respiration rate

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11
Q

Why is it more advantageous to decrease the depth of breathing rather than respiration rate?

A

Due to anatomical dead space
Deep, slow breathing increases alveolar ventilation
Shallow, rapid breathing decreases alveolar ventilation

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12
Q

What 2 factors does transfer of gases between the body and atmosphere depend upon?

A
  • Ventilation - the rate at which gas is passing through the lungs
  • Perfusion - the rate at which blood is passing through the lungs
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13
Q

What results from the fact that blood flow and ventilation vary from bottom to top of the lung?

A

Average arterial and alveolar pressures of oxygen are not exactly the same

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14
Q

At the bottom of the lung, what is V/Q (ventilation: perfusion) ratio?

A

V/Q = <1

There is greater blood flow than ventilation

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15
Q

At the top of the lung, what is V/Q (ventilation: perfusion) ratio?

A

V/Q = >1

There is greater ventilation than blood flow

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16
Q

Why is the match between air in the alveoli and blood in the pulmonary capillaries not always perfect?

A

Due to alveolar dead space

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17
Q

What is alveolar dead space?

A

Ventilated alveoli which are not adequately perfused with blood are considered as alveolar dead space

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18
Q

What is physiological dead space?

A

The sum of anatomical dead space + alveolar dead space

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19
Q

How does the body try to match airflow to blood flow?

A

Local controls acting on smooth muscles of airways and arterioles

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20
Q

What does accumulation of CO2 as a result of increased perfusion result in?

A

Decreases airway resistance (dilation of airways) leading to increased airflow

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21
Q

What does accumulation of O2 as a result of increased ventilation result in?

A

Pulmonary vasodilation which increases blood flow to match airflow

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22
Q

What does O2 decrease in the area result in?

A

Pulmonary vasoconstriction which decreases blood flow to match airflow

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23
Q

What is the effect of decreased O2 on pulmonary and systemic arterioles?

A

Vasoconstriction of pulmonary arterioles

Vasodilation of systemic arterioles

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24
Q

What is the effect of increased O2 on pulmonary and systemic arterioles?

A

Vasodilation of pulmonary arterioles

Vasoconstriction of systemic arterioles

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25
Q

What are four factors that influence the rate of gas exchange across alveolar membranes?

A
  • Partial pressure gradient of O2 and CO2
  • Diffusion coefficient for O2 and CO2
  • Surface area of alveolar membrane
  • Thickness of alveolar membrane
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26
Q

What is partial pressure of a gas (in a mixture of gases that don’t react with each other)?

A

The pressure that that gas exert if it occupied the total volume for the mixture in the absence of other components (at a given temperature)

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27
Q

How do gases move across cell membranes?

A

By a pressure gradient

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28
Q

What determines the pressure gradient for a specific gas?

A

The partial pressure of that gas

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29
Q

What is Dalton’s law of Partial Pressures?

A

The total pressure exerted by a gaseous mixture = the sum of the partial pressure of each individual component in the gas mixture
P(total) = P1 + P2 + …

30
Q

If total pressure of the gas mixture is 100kPa, and half of the mixture is gas 1, what is the partial pressure of gas 1?

A

50 kPa

31
Q

What is the value of total atmospheric pressure?

A

760 mm Hg (101 kPa)

32
Q

What is the partial pressure of N2 in atmospheric air if nitrogen makes up 72% of air?

A

760 x 0.79 = 600 mm Hg (80 kPa)

33
Q

What is the partial pressure of O2 in atmospheric air if oxygen makes up 21% of air?

A

760 x 0.21 = 160 mm Hg (21 kPa)

34
Q

How can an average value for the partial pressure of O2 be worked out when oxygen is continuously diffusing from alveoli into blood?

A

Alveolar Gas Equation

35
Q

What is the alveolar gas equation?

A

PAO2 = PiO2 - (PaCO2/0.8)

PAO2 - partial pressure of O2 in alveolar air
PiO2 - partial pressure of O2 in inspired air
PaCO2 - partial pressure of CO2 in arterial blood

0.8 is the Respiratory Exchange Ratio (RER)

36
Q

What is the air in the respiratory tract saturated with?

A

Water

37
Q

How much does the water vapour pressure contribute to total pressure in the lungs?

A

Around 47 mm Hg

38
Q

What is equation for pressure of inspired air?

A

Inspired air = atmospheric pressure - water vapour pressure

39
Q

What is the value of pressure of inspired air?

A

Inspired air = 760 - 47 = 713 mm Hg at sea level

40
Q

If inspired air pressure is 713 mm Hg, calculate the value of PiO2

A

713 x 0.21 = 150 mm Hg

41
Q

What is the normal value of PCO2

A

40 mm Hg

42
Q

If PiO2 = 150 mm Hg, and PaCO2 = 40 mm Hg, calculate PAO2

A

PAO2 = 150 - (40/0.8)

= 100 mm Hg at sea level

43
Q

In which direction do gases move?

A

From higher to lower partial pressure gradients

44
Q

What is oxygen’s partial pressure gradient?

A

Partial pressure gradient higher in atmosphere than in alveoli

45
Q

Compare the partial pressures of O2 and CO2

A

Partial pressure is much higher for O2 than CO2

46
Q

What is O2 partial pressure gradient from alveoli to blood?

A

100 (in alveoli) - 40 (in blood) mm Hg = 60 mm Hg

47
Q

What is CO2 partial pressure gradient from alveoli to blood?

A

46 - 40 mm Hg = 6 mm Hg

48
Q

What is O2 partial pressure gradient from blood to tissue cell?

A

100 - <40 mm Hg = >60 mm Hg

49
Q

What is CO2 partial pressure gradient from blood to tissue cell?

A

46 - 40 mm Hg = 6 mm Hg

50
Q

If partial pressure gradient for CO2 is much smaller than O2, what offsets the difference in partial pressure gradient?

A

CO2 is more soluble in membranes than O2 - the solubility of gas in membranes is known as the Diffusion Coefficient of the gas

51
Q

What is the Diffusion Coefficient of a gas?

A

The solubility of gas in membranes

52
Q

Compare the diffusion coefficient of O2 and Co2

A

Diffusion coefficient of CO2 is 20 times that of O2

53
Q

Why does a small gradient normally exist been alveolar PO2 (PAO2) and arterial PO2 (PaO2)?

A

Ventilation-perfusion match is usually not perfect

54
Q

What would a big gradient between PAO2 and PaO2 indicate?

A

Problems with gas change in the lungs or a right to left shunt in the heart

55
Q

How do the lungs facilitate effective gas exchange?

A

Provide a very large surface area with thin membranes

56
Q

Describe the effect of surface area and membrane thickness of gas diffusion (Fick’s Law of diffusion)

A

The amount of gas that moves across a sheet of tissue in unit time is proportional to the area of
the sheet but inversely proportional to its thickness

57
Q

How do the airways increase the surface area for gas exchange in the lungs?

A
  • They divide repeatedly

* Small airways form alveoli to increase surface area for gas exchange

58
Q

How is it ensured that the lungs receive a good blood supply for gas exchange?

A

The pulmonary circulation receives the entire cardiac output

59
Q

What are alveoli?

A

Thin-walled inflatable sacs

60
Q

What is the function of alveoli?

A

Gas exchange

61
Q

Describe the structure of alveoli

A

Walls consist of a single layer of flattened Type I alveolar cells

62
Q

What encircles each alveolus?

A

Pulmonary capillaries

63
Q

Describe the effect of partial pressure gradient of O2 and CO2 on rate of gas transfer

A

Rate of transfer increases as partial pressure increases (major influence in rate of gas transfer)

64
Q

Describe the effect of diffusion coefficient on rate of gas transfer

A

Rate of transfer increases as diffusion coefficient increases

65
Q

Describe the effect of surface area of alveolar membrane on rate of gas transfer

A

Rate of transfer increases as surface area increases

66
Q

Describe the effect of thickness of alveolar membrane on rate of gas transfer

A

Rate of transfer decreases as thickness increases

67
Q

What can increase surface area of alveolar membrane?

A

Exercise (deeper breathing expands alveoli and pulmonary capillaries open up when cardiac output increases)

68
Q

What can decrease surface area of alveolar membrane?

A

Emphysema, lung collapse, pneumonectomy

69
Q

What can increase thickness of alveolar membrane?

A

Pulmonary oedema, pulmonary fibrosis, pneumonia

70
Q

List non-respiratory functions of respiratory system

A
  • Route for water loss and heat elimination
  • Enhances venous return
  • Helps maintain normal acid-base balance
  • Enables speech, singing, and other vocalizations
  • Defends against inhaled foreign matter
  • Removes, modifies, activates, or inactivates various materials passing through the pulmonary circulation
  • Nose serves as the organ of smell

Respiratory: Physiology (6 decks)

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