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PHGY 216 mod 3 > Section 2 > Flashcards

Section 2 Flashcards

1
Q

What symbol is used to denote air flow in the respiratory system?

A

In the respiratory system, air flow is denoted by the symbol V.

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2
Q

What is the equation that describes air flow in the respiratory system?

A

The equation for air flow is expressed as Pressure / Resistance = Flow (or diffusion).

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3
Q

What is the driving force for air flow in the respiratory system?

A

The pressure gradient serves as the driving force for air flow in the respiratory system.

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4
Q

What are the three factors that the pressure gradient overcomes for air flow in the respiratory system?

A

The pressure gradient in the respiratory system overcomes the elastance (stiffness) of the respiratory system, the resistance to flow, and the inertia of the system.

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5
Q

What conditions must be met for air to flow into the alveoli?

A

For air to flow into the alveoli, the pressure in the alveoli must be lower than the pressure in the nose.

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6
Q

What conditions must be met for air to flow out of the alveoli?

A

For air to flow out of the alveoli, the pressure in the alveoli must be greater than the pressure in the nose.

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7
Q

What is the focus of understanding alveolar pressure changes in the respiratory system?

A

Understanding respiratory mechanics is the focus of understanding how alveolar pressure changes occur in the respiratory system.

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8
Q

What is atmospheric pressure, and what is another name for it?

A

Atmospheric pressure, also known as barometric pressure (PB), is the pressure exerted by the weight of the air in the atmosphere on the Earth’s surface.

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9
Q

What is the atmospheric pressure at sea level, and how does it change with altitude?

A

At sea level, atmospheric pressure is 760 mmHg, and this value decreases as you gain altitude.

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10
Q

How is atmospheric pressure (PB) treated in the context of the lungs and nose/mouth during standing?

A

Even when standing, there is not enough difference in height between the lungs and the nose/mouth, so atmospheric pressure (PB) is effectively treated as if it were 0.

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11
Q

What is alveolar pressure, and what is another name for it?

A

Alveolar pressure (PA), also known as intrapulmonary pressure, is the pressure in the alveoli.

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12
Q

At the end of inspiration, what is the relationship between alveolar pressure and atmospheric pressure?

A

At the end of inspiration, alveolar pressure is the same as atmospheric pressure, at 0 cm H2O.

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13
Q

What is pleural pressure, and what is another name for it?

A

Pleural pressure (Pp l), also known as intrapleural pressure, is the pressure in the pleural space.

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14
Q

Why is pleural pressure negative to atmospheric pressure, and what is its typical value?

A

Pleural pressure is negative to atmospheric pressure because the lungs want to collapse while the chest wall wants to expand. Its typical value is around -5 cm H2O.

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15
Q

What is transpulmonary pressure, and what is another name for it?

A

Transpulmonary pressure (Pt p), also referred to as lung recoil pressure (Pl) or transmural pressure, is the difference between alveolar pressure and pleural pressure.

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16
Q

what is Intrathoracic Pressure?

A

the pressure within the thoracic cavity

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17
Q

What are the traditional units used for expressing pressures in respiratory physiology?

A

The traditional units for expressing pressures in respiratory physiology are based on the height of a column of mercury (mmHg) or water (cm H2O).

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18
Q

When discussing diffusion in respiratory physiology, which unit is commonly used for partial pressures of gases?

A

mmHg is commonly used for the partial pressures of gases when discussing diffusion in respiratory physiology.

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19
Q

What unit is preferred when discussing bulk flow (convection) in respiratory physiology, and why?

A

cm H2O is preferred when discussing bulk flow (convection) in respiratory physiology because the pressures needed to generate flow are typically small, and cm H2O provides a more practical scale.

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20
Q

Why is cm H2O used instead of mmHg for pressures related to bulk flow in respiratory physiology?

A

cm H2O is used because the pressures needed for bulk flow are typically small, and cm H2O is more practical. For example, a pressure of 5 cm H2O equals ~3.7 mmHg.

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21
Q

What is a manometer, and what is its function in respiratory physiology?

A

A manometer is a device used to measure pressures. It is employed in respiratory physiology to quantify various pressures.

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22
Q

How are pressures related to convective flow expressed in respiratory physiology?

A

Pressures related to convective flow are expressed relative to atmospheric pressure. For instance, an alveolar pressure of 1029 cm H2O, with an atmospheric pressure of 1034 cm H2O, is referred to as -5 cm H2O.

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23
Q

Why are some pressures referred to as “negative” in respiratory physiology, and do negative pressures exist?

A

“Negative” pressures in respiratory physiology are less than the barometric pressure to which they are referred. Negative pressures are a relative term, and they do not truly exist; they are less than the reference pressure.

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24
Q

What is a crucial property of the lungs related to their tendency to deflate following inflation?

A

A crucial property of the lungs is their intrinsic tendency to deflate following inflation.

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25
Q

What are the two factors contributing to the intrinsic tendency of the lungs to deflate?

A

The intrinsic tendency of the lungs to deflate is due to elastin fibers and surface tension.

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26
Q

What is the role of elastin fibers in lung behavior?

A

Elastin fibers within the lung’s connective tissues form a meshwork that enhances elastic behavior. When the lung is stretched during inhalation, the elastic recoil of elastin fibers causes the lung to deflate.

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27
Q

What is surface tension in the context of the lung’s elastic recoil?

A

: Surface tension is the force exerted by the liquid lining the inside of the alveoli and accounts for about 70% of the elastic recoil properties of the lung.

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28
Q

How does surface tension resist forces that try to increase its area?

A

The liquid layer’s surface tension resists forces that try to increase its area because water molecules resist being pulled apart.

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29
Q

What effect does surface tension have on the surface area of the liquid lining the alveoli?

A

Surface tension causes the surface area of the liquid lining the alveoli to shrink as much as possible because water molecules are strongly attracted to each other.

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30
Q

In the absence of expanding forces, what happens to the alveoli due to surface tension?

A

In the absence of expanding forces, the alveoli shrink as much as possible due to the surface tension of the liquid lining, leading to the expulsion of alveolar gas.

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31
Q

Why do alveoli not collapse despite the strong influence of surface tension?

A

Alveoli do not collapse due to the presence of pulmonary surfactant and alveolar interdependence.

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32
Q

What would happen to alveoli if the surface liquid consisted only of water?

A

If the surface liquid were water alone, alveoli would collapse, and the pressure required to open them upon inspiration would be much greater.

33
Q

What is pulmonary surfactant, and what is its role in preventing alveolar collapse?

A

Pulmonary surfactant is a complex mixture of lipids and proteins secreted by type II alveolar cells. It disperses water molecules on the surface of alveoli, reducing water-water attractions and decreasing alveolar surface tension.

This is crucial for respiratory mechanics, making inflation easier (increasing compliance) and reducing surface tension more in smaller alveoli than in larger ones.

34
Q

How does alveolar interdependence contribute to preventing alveolar collapse?

A

Alveolar interdependence refers to the connection of each alveolus to its surrounding alveoli by connective tissues. If one alveolus starts to collapse, it is supported by its neighbors. As the neighboring alveoli recoil, they pull outward on the collapsing alveolus, helping to prevent it from collapsing.

35
Q

What happens when an alveolus in a group of interconnected alveoli starts to collapse?

A

When an alveolus in a group of interconnected alveoli starts to collapse, the surrounding alveoli are stretched by the collapsing alveolus.

36
Q

How do the neighboring alveoli help prevent the collapsing alveolus from collapsing further?

A

As the neighboring alveoli recoil, they pull outward on the collapsing alveolus, helping prevent it from collapsing further.

37
Q

What challenge arises from the differences in alveolar size in the lung despite the large surface area for gas exchange?

A

The differences in alveolar size can create problems for alveolar stability.

38
Q

What is the primary force working to collapse the alveoli, and what causes this force?

A

The inward forces of alveolar surface tension are working to collapse the alveoli. Surface tension results from the liquid lining the inside of the alveoli.

39
Q

What does the Law of Laplace state?

A

The Law of Laplace states that the magnitude of the collapsing pressure is directly proportional to the surface tension and inversely proportional to the radius of the alveoli.

40
Q

What is the equation representing the Law of Laplace?

A

The equation representing the Law of Laplace is

2T(surface tension) / r(alveolar radius)
= P (collapsing pressure).

41
Q

How does surface tension and alveolar radius influence the collapsing pressure according to the Law of Laplace?

A

According to the Law of Laplace, the collapsing pressure is directly proportional to surface tension and inversely proportional to the radius of the alveoli.

42
Q

if the surface tensions of two alveoli, Alveolus 1 and Alveolus 2, were equivalent, but Alveolus 2 had double the radius of Alveolus 1, which alveolus would have the
larger inward-directed pressure?

A

Alveolus 1

43
Q

when two alveoli with the same surface tension but different radii
are connected by the same terminal airway, the smaller alveolus will collapse and empty into the larger alveoli. However, this would be detrimental to lung function if it were to occur.

How do you think this might be prevented?
a) Small alveoli contain more elastin fibres
b) Small alveolus will secrete more surfactant
c) Small alveoli are always surrounded by many other alveoli

A

b)

In order to prevent collapse, small alveoli secrete more surfactant! This is because pulmonary surfactant decreases surface tension, thus decreasing the collapsing pressure.

44
Q

Explain in your own words what pulmonary surfactant is and how it helps to prevent alveolar collapse. What other factors contribute to the maintenance of alveolar structure?

A

Pulmonary surfactant is a compound composed of a mixture of lipids and proteins, and is produced and secreted by alveolar cells onto the surface of alveoli. The hydrophobicity of surfactant enables it to interfere with the attractive intermolecular forces between the water molecules found lining the alveoli, thus reducing surface tension.

Each alveolus is able to regulate the amount of pulmonary surfactant it secretes, allowing each alveoli to moderate its surface tension. This means that all alveoli, even with differences in size, are able to equalize their collapsing pressures. This is essential for the lung to maintain maximum gas exchange surface area at all times.

Other than surfactant, alveolar interdependence, which is the supportive recoil of neighbouring alveoli, helps to maintain alveolar structure and prevent collapse.

45
Q

__ = the pressure in the alveoli. It is 0 cm H2O

A

PA

46
Q

___ = The pressure exerted by the weight of the air in the atmosphere on the Earth’s surface. For
simplicity, it is 0 cm H2O

A

PB

47
Q

___ = This is the pressure in the pleural space and it closely approximates the intrathoracic
pressure. It is normally around -5 cm H2O

A

Ppl

48
Q

___ = The difference between the alveolar pressure and the pleural pressure. It is also referred to
as lung recoil pressure (Pl).

A

Ptp

49
Q

What condition must be met for air to flow into the alveoli, and what for air to flow out?

A

For air to flow into the alveoli, alveolar pressure must be less than atmospheric pressure. For air to flow out of the alveoli, alveolar pressure must be greater than atmospheric pressure.

50
Q

Why does alveolar pressure need to change to generate a pressure gradient for air flow?

A

Atmospheric pressure is essentially fixed at 0 mmHg, so alveolar pressure must change to generate the necessary pressure gradient for air flow.

51
Q

What is the equation relating alveolar pressure (PA), pleural pressure (Pp l), and lung recoil pressure (Pi)?

A

Alveolar Pressure (PA) - Pleural Pressure (Pp l) = Lung Recoil Pressure (Pi)

52
Q

To change alveolar pressure (PA), what factors can be altered according to an equation?

A

To change alveolar pressure (PA), either lung recoil pressure (Pi), pleural pressure (Pp l), or both must be altered.

53
Q

Why can’t lung volume be changed by altering lung recoil pressure (Pi)?

A

Lung recoil pressure (Pi) depends on lung volume, so changing a pressure reflecting lung volume cannot effectively change lung volume.

54
Q

How do the muscles in the chest wall contribute to changing alveolar pressure?

A

Activating the inspiratory muscles decreases pleural pressure (Pp l), which decreases alveolar pressure (PA), allowing air to flow into the alveoli. Activation of the expiratory muscles has the opposite effect, allowing expulsion of air from the alveoli.

55
Q

When does flow occur during the respiratory cycle, and why?

A

Flow occurs during the respiratory cycle when there is a pressure gradient from the atmosphere to the alveoli. Flow starts during inspiration when a pressure gradient is established.

56
Q

What is the condition of alveolar pressure at the end of expiration?

A

At the end of expiration, alveolar pressure equals atmospheric pressure, resulting in no flow.

57
Q

What establishes the pressure gradient during inspiration, and what is the direction of the gradient?

A

The pressure gradient during inspiration is established by the contraction of inspiratory muscles, creating a gradient from atmosphere to alveoli.

58
Q

How does inspiration end, and what allows lung recoil pressure to equal pleural pressure?

A

Inspiration ends as the contraction of inspiratory muscles decreases, allowing lung recoil pressure to catch up to and equal pleural pressure.

59
Q

When does expiration start, and what is the condition of lung recoil pressure and pleural pressure?

A

Expiration starts when inspiratory muscles have stopped contracting. Lung recoil pressure is now greater than pleural pressure, resulting in a positive alveolar pressure.

60
Q

What is the result of the positive alveolar pressure during expiration?

A

The positive alveolar pressure during expiration leads to expiratory flow.

61
Q

What is the initial condition of alveolar pressure before inhalation, and why is there no flow at this point?

A

Before inhalation, alveolar pressure equals atmospheric pressure, and there is no flow of air in or out of the lungs.

62
Q

What causes the pleural pressure to decrease during the onset of inhalation, and what is its effect on alveolar pressure?

A

Contraction of the inspiratory muscles causes the pleural pressure to decrease, enlarging the thoracic cavity. This decrease in pleural pressure lowers alveolar pressure, allowing air to flow into the lungs.

63
Q

Why is it noted that the change in pleural pressure is not linear during the onset of inhalation?

A

At the onset of inspiration, there is an increased resistance to flow that pleural pressure must overcome.

64
Q

What happens at the end of inspiration, and how does alveolar pressure change?

A

At the end of inspiration, the inspiratory muscles relax, increasing pleural pressure and alveolar pressure. Air flows from the lungs until alveolar pressure equals atmospheric pressure.

65
Q

Is the activation of expiratory muscles necessary for normal expiration, and why?

A

Activation of expiratory muscles is not necessary for normal expiration due to the strong recoil forces.

66
Q

What distinguishes active expiration from passive expiration, and when might active expiration be used?

A

Active expiration involves the activation of expiratory muscles and can be used during exercise when high levels of ventilation are necessary.

67
Q

How does active expiration occur during routine exercise, and what muscles are involved?

A

During routine exercise, active expiration involves the contraction of expiratory muscles of the abdominal wall. Increased abdominal pressure is transferred to the pleural space, increasing pleural pressure. Contraction of the internal intercostals helps decrease the size of the thoracic cavity.

68
Q

What happens during forced expiration, and what is the equal pressure point?

A

In forced expiration, a person activates expiratory muscles to generate high pleural pressure. As expiratory flow continues, the equal pressure point is reached, where the pressure within the airways equals pleural pressure. Past this point, increased effort doesn’t increase flow due to airway compression. The pressure gradient generating flow is the recoil pressure of the lungs (PA - Pl).

69
Q

Using what you know about pleural pressure and the formula PA = Pl + Ppl, explain in your own words why the lungs do not collapse during active expiration

A

During active expiration, pleural pressure becomes positive due to the increased abdominal pressure, but the lungs do not collapse. This occurs because the alveolar pressure increases correspondingly.

Also, any pressure increase in the pleural pressure is offset by a proportionate increase in airway resistance due to the compression of the airways. This blocks further outflow and, as such, active expiration never results in a
person exhaling past their physiological residual volume (which would collapse the bronchioles)

70
Q

What does the pressure-volume relationship in the lung show throughout the cycle of inspiration and expiration?

A

The pressure-volume relationship in the lung demonstrates differences in pressure, volume, and lung volumes throughout the cycle of inspiration and expiration.

71
Q

How does pleural pressure (Pl) change with lung volume, and what are the extremes in pressure values?

A

As lung volume increases, pleural pressure (Pl) increases from about 0 cm H2O at residual volume to about 30 cm H2O at total lung capacity.

72
Q

What is Pr s, and how is it derived?

A

Pr s is the combined pressure-volume relationship of the respiratory system and is derived by combining pleural pressure (Pl) and pressure of the chest wall (Pw).

73
Q

How does the pressure of the chest wall (Pw) function in terms of lung volume?

A

The pressure of the chest wall (Pw) functions like a spring. Below about 65% of total vital capacity, the compressed spring exerts negative (inflating) pressures, yet at 100% total vital capacity, the chest wall, now a stretched spring, wants to collapse.

74
Q

What is compliance, and how is it derived from the pressure-volume curve?

A

Compliance is the slope of the pressure-volume curve. It is derived from the relationship between pressure and volume in the respiratory system.

75
Q

Where is compliance greatest on the pressure-volume curve, and what does this imply about the work needed for breathing?

A

Compliance is greatest at functional residual capacity, implying that the amount of work or pressure needed to either inhale or exhale is at its minimum.

76
Q

How does low compliance affect the pressure required to move air in or out, and what conditions may result in low compliance?

A

Low compliance means more pressure is required to move air in or out. Conditions like emphysema, where compliance is decreased, result in significantly greater work required for breathing even at functional residual volume.

77
Q

Define Compliance in the context of the respiratory system.

A

Compliance is the ability of the lung to stretch so that at functional residual capacity, it is easy to move air in or out of the lungs.

78
Q
A

PHGY 216 mod 3 (9 decks)

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