Respiratory Physiology (Part 2) Flashcards Preview

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Flashcards in Respiratory Physiology (Part 2) Deck (98):
1

What are the 3 muscles of inspiration?

- diaphragm
- external intercostal
- accessory muscles such as the sternocleidomastoid

*diaphragm is the most important

2

What drives expiration?

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

3

What muscles drive forced expiration?

- abdominal muscles
- internal intercostal muscles

4

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

the lungs and chest wall

5

What does compliance describe?

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

6

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

their elastic properties, or elastance

7

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

lower

8

Pressures equal to atmospheric pressure are ____.

zero

9

Pressures higher than atmospheric pressure are ____.

positive

10

Pressures lower than atmospheric pressure are ____.

negative

11

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

the compliance of the lung

12

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

inflates

increases

13

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

expanding pressure

14

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

insipration

15

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

less

expiration

16

Describe the phenomenon of hysteresis

The slopes of the inspiration and expiration limbs are different

17

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

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

18

Compliance is measured on the _____ limb

expiration

19

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

Because of the surface tension at the liquid-air interface

20

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

increase

21

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

decrease

22

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

a pneumothorax

23

Normally the intrapleural space has a _____ pressure

negative

24

What creates this negative intrapleural pressure?

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

25

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

zero

26

What are the 2 consequences of a pneumothorax?

1) the lungs collapse
2) the chest wall springs out

27

What is the problem keeping small alveoli open?

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

28

What does the Law of Laplace state?

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

29

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

low

minimal

30

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

high

more

31

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

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

32

How do small alveoli remain open under high collapsing pressures?

surfactant

33

What is surfactant?

a mixture of phospholipids that line the alveoli

34

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

By reducing surface tension

35

What is another advantage surfactant provides for pulmonary function?

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

36

How do you calculate airflow?

Q = ΔP/R

Q = Airflow
ΔP = Pressure gradient
R = Airway resistance

37

What is the driving force for airflow?

pressure difference

38

What is the site of highest airway resistance?

the medium-sized bronchi

39

What innervates bronchial smooth muscle?

parasympathetic cholinergic nerve fibers

40

Parasympathetic stimulation of bronchial smooth muscle produces _____.

constriction

41

Sympathetic stimulation of bronchial smooth muscle produces _____.

relaxation

42

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

decreases

increases

43

What are the 3 phases of the breathing cycle?

- rest
- inspiration
- expiration

44

What does alveolar pressure equal at rest?

zero (atmospheric pressure)

45

What does intrapleural pressure equal at rest?

It is negative at approximately -5

46

What happens to alveolar pressure during inspiration?

It becomes negative (lower than atmospheric pressure)

47

What happens to intrapleural pressure during inspiration?

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

48

What happens to alveolar pressure during expiration?

It becomes positive (higher than atmospheric pressure)

49

What happens to intrapleural pressure during expiration?

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

50

What does gas exchange in the respiratory system refer to?

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

51

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

simple diffusion

52

Net diffusion of a gas is dependent on what?

the concentration gradient

53

What does gas pressure in a mixture of gases equal?

Sum of the “Partial Pressures” of Individual Gases

54

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

- Concentration
- Solubility coefficient of the gas

55

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

directly

inversely

56

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

greater

57

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

- Dissolved gas
- Bound gas
- Chemically modified gas

58

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

dissolved

59

Where does gas exchange occur?

Between alveolar gas and the pulmonary capillary

60

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

O2

CO2

61

What is the PO2 and PCO2 in dry inspired air?

PO2 is approximately 160 mmHg

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

62

In humidified air the air is fully saturated with what?

water vapor

63

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

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

64

What is the PCO2 in humidified air in the trachea?

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

65

What is the PO2 and PCO2 in alveolar air?

PO2 is 100 mmHg

PCO2 is 40 mmHg

66

Why does PO2 decrease and PCO2 decrease in the alveoli?

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

67

Blood entering the pulmonary capillaries is essentially ___ ____ blood

mixed venous blood

68

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

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

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

systemic arterial blood

70

What is the PO2 and PCO2 in system arterial blood?

PO2 is 100 mmHg

PCO2 is 40 mmHg

71

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

- dissolved
- bound to hemoglobin

72

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

2%

73

Dissolved O2 produces what?

partial pressure

74

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

No

75

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

98

76

Describe the structure of hemoglobin

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

What is adult hemoglobin called?

alpha2beta2

78

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

4, one per subunit

79

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

the ferrous (Fe2+) state

80

What are 3 variants of the hemoglobin molecule?

- Methemoglobin
- Fetal hemoglobin
- Hemoglobin S

81

When is hemoglobin considered methemoglobin?

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

82

Does methemoglobin bind oxygen?

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

83

Describe the fetal hemoglobin variant

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

84

What is the physiologic consequence of the fetal hemoglobin modification?

It has a higher affinity for O2

85

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

sickle cell disease

86

Which subunits are abnormal in hemoglobin S?

the beta subunits

87

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

occlusion of small blood vessels

88

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

less

89

What is O2-binding capacity?

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

90

What is O2 content?

The actual amount of O2 per volume of blood

91

How is O2 content calculated?

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

92

What determines O2 delivery to tissues?

Blood flow and the O2 content of blood

93

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

= Cardiac output x O2 content of blood

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

94

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

100%

95

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

75%

96

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

50

97

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

25

98

Percent saturation of hemoglobin is a function of what?

PO2