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630: Medical Physiology > Respiratory Physiology (Part 2) > Flashcards

Respiratory Physiology (Part 2) Flashcards

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USMLE® Step 1 flashcards
1
Q

What are the 3 muscles of inspiration?

A
  • diaphragm
  • external intercostal
  • accessory muscles such as the sternocleidomastoid

*diaphragm is the most important

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2
Q

What drives expiration?

A

It is a passive process driven by the reverse pressure gradient between the lungs and atmosphere

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3
Q

What muscles drive forced expiration?

A
  • abdominal muscles

- internal intercostal muscles

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4
Q

The compliance of what 2 structures are of primary interest in the respiratory system?

A

the lungs and chest wall

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5
Q

What does compliance describe?

A

The change in lung volume for a given change in pressure, which can be defined as the system’s distensibility

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6
Q

The compliance of the lungs and chest wall are inversely correlated with what?

A

their elastic properties, or elastance

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7
Q

The greater the amount of elastic tissue, the greater the elastic force, but the _____ the compliance

A

lower

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8
Q

Pressures equal to atmospheric pressure are ____.

A

zero

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9
Q

Pressures higher than atmospheric pressure are ____.

A

positive

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10
Q

Pressures lower than atmospheric pressure are ____.

A

negative

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11
Q

What does the slope of the pressure-volume loop equal?

A

the compliance of the lung

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12
Q

As pressure outside of the lungs becomes more negative, the lung ____ and its volume _____.

A

inflates

increases

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13
Q

What is the negative pressure outside of the lungs that causes them to inflate called?

A

expanding pressure

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14
Q

The lungs fill with air along the _____ limb of the pressure-volume loop

A

insipration

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15
Q

Once the lungs are expanded maximally, the pressure outside of the lungs is made gradually ____ negative, causing the lung volume to decrease along the _____ limb of the pressure-volume loop

A

less

expiration

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16
Q

Describe the phenomenon of hysteresis

A

The slopes of the inspiration and expiration limbs are different

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17
Q

Which limb on the pressure-volume loop is greater for a given outside pressure? Why?

A

the expiration limb, because compliance is higher during expiration than during inspiration

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18
Q

Compliance is measured on the _____ limb

A

expiration

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19
Q

Why are the inspiration and expiration limbs of the lung compliance curve different?

A

Because of the surface tension at the liquid-air interface

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20
Q

As surfactant density increases, surface tension decreases which causes a(n) _____ in compliance

A

increase

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21
Q

As surfactant density decreases, surface tension increases which causes a(n) _____ in compliance

A

decrease

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22
Q

What is created when air is introduced into the intrapleural space?

A

a pneumothorax

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23
Q

Normally the intrapleural space has a _____ pressure

A

negative

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24
Q

What creates this negative intrapleural pressure?

A

2 opposing elastic forces pulling on the intrapleural space: the lungs tend to collapse and the chest wall which tends to spring out

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25
Q

When a pneumothorax is introduced, the normal negative intrapleural pressure becomes ____.

A

zero

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26
Q

What are the 2 consequences of a pneumothorax?

A

1) the lungs collapse

2) the chest wall springs out

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27
Q

What is the problem keeping small alveoli open?

A

The attractive forces between adjacent molecules of liquid creates surface tension. As the molecules of liquid are drawn together, the surface area becomes as small as possible, forming a sphere. The surface tension generates a pressure that tends to collapse the sphere

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28
Q

What does the Law of Laplace state?

A

The pressure tending to collapse an alveolus is directly proportional to the surface tension generated by the molecules of liquid lining the alveolus and inversely proportional to alveolar radius

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29
Q

A large alveolus will have a ___ collapsing pressure, and therefore will require ____ pressure to keep it open

A

low

minimal

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30
Q

A small alveolus will have a ___ collapsing pressure, and therefore will require ____ pressure to keep it open

A

high

more

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31
Q

So, why are alveoli so small if they have a higher tendency to collapse?

A

They need to be as small as possible to increase their total surface area for gas exchange

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32
Q

How do small alveoli remain open under high collapsing pressures?

A

surfactant

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33
Q

What is surfactant?

A

a mixture of phospholipids that line the alveoli

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34
Q

How does surfactant reduce the collapsing pressure for a given radius?

A

By reducing surface tension

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35
Q

What is another advantage surfactant provides for pulmonary function?

A

It increases lung compliance, which reduces the work of expanding the lungs during inspiration

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36
Q

How do you calculate airflow?

A

Q = ΔP/R

Q = Airflow
ΔP = Pressure gradient
R = Airway resistance
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37
Q

What is the driving force for airflow?

A

pressure difference

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38
Q

What is the site of highest airway resistance?

A

the medium-sized bronchi

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39
Q

What innervates bronchial smooth muscle?

A

parasympathetic cholinergic nerve fibers

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40
Q

Parasympathetic stimulation of bronchial smooth muscle produces _____.

A

constriction

41
Q

Sympathetic stimulation of bronchial smooth muscle produces _____.

A

relaxation

42
Q

High lung volumes ____ airway resistance, whereas low lung volumes ____ airway resistance.

A

decreases

increases

43
Q

What are the 3 phases of the breathing cycle?

A
  • rest
  • inspiration
  • expiration
44
Q

What does alveolar pressure equal at rest?

A

zero (atmospheric pressure)

45
Q

What does intrapleural pressure equal at rest?

A

It is negative at approximately -5

46
Q

What happens to alveolar pressure during inspiration?

A

It becomes negative (lower than atmospheric pressure)

47
Q

What happens to intrapleural pressure during inspiration?

A

it becomes even more negative than at rest (approximately -8)

48
Q

What happens to alveolar pressure during expiration?

A

It becomes positive (higher than atmospheric pressure)

49
Q

What happens to intrapleural pressure during expiration?

A

It begins to return to the value at rest (-5) so it becomes more positive

50
Q

What does gas exchange in the respiratory system refer to?

A

Diffusion of O2 and CO2 in the lungs and in the peripheral tissues

51
Q

The transfer of gases across cell membranes or capillary walls occurs by way of what?

A

simple diffusion

52
Q

Net diffusion of a gas is dependent on what?

A

the concentration gradient

53
Q

What does gas pressure in a mixture of gases equal?

A

Sum of the “Partial Pressures” of Individual Gases

54
Q

What are the 2 factors that determine the partial pressure of a gas dissolved in a fluid?

A
  • Concentration

- Solubility coefficient of the gas

55
Q

Partial pressure of a gas dissolved in fluid is _____ related to concentration of the dissolved gas and _____ related to the solubility coefficient

A

directly

inversely

56
Q

For a given concentration, the less soluble the gas, the _____ the partial pressure

A

greater

57
Q

The total gas concentration in solution is the sum of what 3 things?

A
  • Dissolved gas
  • Bound gas
  • Chemically modified gas
58
Q

In solution, only _____ gas molecules contribute to the partial pressure

A

dissolved

59
Q

Where does gas exchange occur?

A

Between alveolar gas and the pulmonary capillary

60
Q

__ diffuses from alveolar gas into pulmonary capillary blood, and __ diffuse from pulmonary capillary blood into alveolar gas.

A

O2

CO2

61
Q

What is the PO2 and PCO2 in dry inspired air?

A

PO2 is approximately 160 mmHg

PCO2 is zero, because there is no CO2 in dry inspired air

62
Q

In humidified air the air is fully saturated with what?

A

water vapor

63
Q

What happens to PO2 when air is humidified in the trachea?

A

It is reduced, because O2 is “diluted” by water vapor and equals approximately 150 mmHg

64
Q

What is the PCO2 in humidified air in the trachea?

A

PCO2 is zero, because there is no CO2 in dry inspired air

65
Q

What is the PO2 and PCO2 in alveolar air?

A

PO2 is 100 mmHg

PCO2 is 40 mmHg

66
Q

Why does PO2 decrease and PCO2 decrease in the alveoli?

A

Because O2 leaves alveolar air and is added to pulmonary capillary blood, and CO2 leaves pulmonary capillary blood and enters alveolar air

67
Q

Blood entering the pulmonary capillaries is essentially ___ ____ blood

A

mixed venous blood

68
Q

What does PO2 and PCO2 equal in the mixed venous blood of the pulmonary capillaries? Explain the reasoning behind each

A

PO2 is 40 mmHg because the tissues have taken up and consumed O2

PCO2 is 46 mmHg because the tissues have produced CO2 and added it to venous blood

69
Q

The blood that leaves the pulmonary capillaries will become ___ ____ blood

A

systemic arterial blood

70
Q

What is the PO2 and PCO2 in system arterial blood?

A

PO2 is 100 mmHg

PCO2 is 40 mmHg

71
Q

What are the 2 forms in which O2 is carried in blood?

A
  • dissolved

- bound to hemoglobin

72
Q

Dissolved O2 accounts for approximately _% of the total O2 content of blood

A

2%

73
Q

Dissolved O2 produces what?

A

partial pressure

74
Q

Is the amount of dissolved O2 sufficient enough to meet the demands of the tissues?

A

No

75
Q

O2 bound to hemoglobin accounts for approximately _% of the total O2 content of blood

A

98

76
Q

Describe the structure of hemoglobin

A

It is a globular protein that consists of 4 subunits, in which each contains a heme moiety made up of an iron-binding porphyrin and a polypetide chain, which is designated as either alpha or beta

77
Q

What is adult hemoglobin called?

A

alpha2beta2

78
Q

How many molecules of O2 can bind to a single hemoglobin molecule?

A

4, one per subunit

79
Q

In order for hemoglobin to bind O2 it must be in what state?

A

the ferrous (Fe2+) state

80
Q

What are 3 variants of the hemoglobin molecule?

A
  • Methemoglobin
  • Fetal hemoglobin
  • Hemoglobin S
81
Q

When is hemoglobin considered methemoglobin?

A

When the heme moieties is in the ferric state (Fe3+)

82
Q

Does methemoglobin bind oxygen?

A

No, because it is not in the ferrous state, it is in the ferric state

83
Q

Describe the fetal hemoglobin variant

A

The 2 beta chanins are replaced by gamma chains, giving it the designation of alpha2gamma2

84
Q

What is the physiologic consequence of the fetal hemoglobin modification?

A

It has a higher affinity for O2

85
Q

Hemoglobin S is an abnormal variant of hemoglobin that causes what disease?

A

sickle cell disease

86
Q

Which subunits are abnormal in hemoglobin S?

A

the beta subunits

87
Q

The deformation of hemoglobin S in its deoxygenated form can result in what?

A

occlusion of small blood vessels

88
Q

The O2 affinity of hemoglobin S is ___ than the O2 affinity of hemoglobin A.

A

less

89
Q

What is O2-binding capacity?

A

The maximum amount of O2 that can be bound to hemoglobin per volume of blood, assuming hemoglobin is 100% saturated

90
Q

What is O2 content?

A

The actual amount of O2 per volume of blood

91
Q

How is O2 content calculated?

A

O2 content = O2 binding capacity x % Saturation + Dissolved O2

92
Q

What determines O2 delivery to tissues?

A

Blood flow and the O2 content of blood

93
Q

What are the 2 ways O2 delivery to tissues can be calculated?

A

= Cardiac output x O2 content of blood

= Cardiac output x (Dissolved O2 + O2 bound to hemoglobin)

94
Q

If 4 molecules of O2 are bound to heme groups than saturation is __%

A

100%

95
Q

If 3 molecules of O2 are bound to heme groups than saturation is __%

A

75%

96
Q

If 2 molecules of O2 are bound to heme groups than saturation is __%

A

50

97
Q

If 1 molecules of O2 are bound to heme groups than saturation is __%

A

25

98
Q

Percent saturation of hemoglobin is a function of what?

A

PO2

630: Medical Physiology (24 decks)

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