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Respiratory System > Mechanisms of Breathing I & II > Flashcards

Mechanisms of Breathing I & II Flashcards

1
Q

How does air move within the respiratory system?

A

The respiratory system achieves movement of air due to the ability of gases to naturally move from (connected) areas of higher to lower pressure, until an equilibrium is reached again

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2
Q

What are the two ways to quantify pressure?

A

PV = nRT

P ∝ n/v

if n remains constant, inc. volume = decreased pressure

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3
Q

Explain the effects of change in lung volume

A

Change in lung volume induces changes in alveolar pressure
=> generates pressure gradients between alveoli and
atmosphere, causing air flow

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4
Q

Describe the movement of the respiratory system during inspiration

A

Diaphragm contracts
Thoracic cavity expands
Alveolar pressure decreases
Air moves in

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5
Q

What movement occurs within the respiratory system during expiration?

A

Diaphragm relaxes
Thoracic cavity volume decreases
Alveolar pressure increases
Air moves out

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6
Q

How is lung pressure altered to create pressure gradients during the mechanism of breathing?

A

Inhalation: atm > lung
Exhalation: atm < lung

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7
Q

How is a pressure gradient created within the lungs?

A

Achieved by manipulating lung volume

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8
Q

What causes lung volume to be altered within the respiratory system?

A

Contraction of respiratory muscles induces volume changes in the thoracic cavity, causing pressure changes in the lungs
- pressure gradient created between atm and lungs
=> air moves

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9
Q

When is equal pressure reached in the respiratory system?

A

At the end of expiration, P(alveoli) = P(atm) so there is no movement of air as no pressure gradient

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10
Q

Describe the pressure gradient during inspiration

A

Outer (parietal membranes) surfaces of the lung are pulled outwards (expansion)

  • increases volume
  • decreases pressure

P(alveoli) < P(atm)
air flows in from atm to low pressure in lungs

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11
Q

Describe the pressure gradient during expiration

A

Air in the lungs is compressed

  • decreased volume
  • increased pressure

P(alveoli) > P(atm)
Air flows out of high pressure lungs to low pressure in atm

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12
Q

What is the role of the pleural cavity?

A

Indirectly attaches the lungs and chest wall

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13
Q

What is the pleural cavity?

A

Fluid filled space between membranes (pleura); lines each lung and the chest wall

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14
Q

What is the function of the pleura?

A

Help reduce friction to aid movement of the lungs

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15
Q

What causes negative pressure to build up in the pleural cavity?

A

The opposing elastic recoil of the chest wall (outwards) and lungs (inwards), generates negative pressure within the pleural cavity

sealed cavity + increased vol. = decreased pressure

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16
Q

What is the effect of the negative pressure in the pleural cavity?

A

Pulls the two membranes together

more negative the pressure = more force pulling pleurae together

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17
Q

What is the stability of pressure like between neighbouring spaces?

A

Differences in pressure between neighbouring spaces are unstable

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18
Q

What is the effect of insufficient opposing force in the pleural cavity?

A

Equilibrium will be re-established via either:
- movement of liquid / gas
- collapse / expansion of volume at the expense of
surrounding structures

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19
Q

What is negative pressure?

A

Lower no. of molecules per volume (relative to surroundings)
-> generates collapsing force by pulling surfaces of
contained spaces together

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20
Q

What is positive pressure?

A

Increased no. of molecules per volume (relative to surroundings)
-> generates an expanding force by pushing surfaces of
contained spaces apart

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21
Q

What is the effect of equal pressures?

A

Equilibrium reached

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22
Q

Explain the effect of increasing the volume of the pleural cavity

A

Decreases pressure further = negative pressure
- Collapsing force exerted on lung at expense of lung
volume; draws air in

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23
Q

What is the effect of positive pressure on on the lungs and pleural cavity?

A

Increasing pressure of the lungs (decreased vol.) compresses the pleural membrane
Expanding force exerted on the lungs (inwards) so air moves out

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24
Q

What determines the degree of expansion and retraction of the lungs?

A

Expansion and retraction of the lung is determined by the relative size of the opposing forces

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25
What is the pressure gradient like at the end of expiration?
At the end of expiration, the system is in equilibrium | - forces are equal
26
Why is intrapleural pressure slightly negative after expiration?
At the end of expiration, the intra-pleural pressure is slightly negative due to minor stretching of the cavity by the opposing recoil forces acting on each pleura
27
What occurs in the intrapleural membranes for lung volume to change?
Either forces acting on one of the pleura needs to become greater than the other
28
Describe the events occurring during inspiration in the pleural cavity and lungs
``` Muscular contraction (e.g. diaphragm) Parietal pleura pulled outwards Cavity stretches - inc. vol, decreased P(intrapleural) ```
29
What is the effect of decreased P(intrapleural)?
The decreased (more negative) P(intrapleural) creates a greater level of force acting to pull the visceral pleura outwards
30
What enables the parietal pleura to be held outwards?
Parietal pleura held outwards by muscular contraction
31
What causes the parietal pleura to pulled outwards?
Outward force generated by P(intrapleural) > Inward force generated by lung recoil, expanding the lung
32
Describe the events occurring during passive expiration
Relaxation of previously contracted muscles Reduces outwards force on parietal pleura Reduces degree of cavity stretch P(intrapleural) increases
33
Explain the effect of the increased P(intrapleural)
``` Increased P(intrapleural) no longer generates sufficient force to overcome elastic recoil of visceral pleura inwards Lung volume decreases - air moves out ```
34
What happens during a forced expiration?
Other respiratory muscles also contract (e.g. abdominal and intercostal) provide further inward force on parietal pleura Pleural cavity compressed further increasing P(intrapleural) forcing an increased lung volume decline
35
How is movement of air into / out of lungs achieved?
By altering the volume of the thoracic cavity
36
Outline the events within the thoracic cavity during inspiration
- Respiratory muscles contract - Thoracic cavity volume increases - P(intrapleural) = more negative - Outward force on visceral pleura > inward recoil force - Lungs expand, increasing Volume - Palv < Patm - air moves into alveoli expanding lungs
37
Which mechanisms are involved in expiration?
Involves the elastic recoil of lungs and muscle relaxation
38
What causes lung compression during expiration?
Increased P(intrapleural) - during forced expiration
39
Why does passive expiration not require an increased P(intrapleural)?
Elastic recoil is sufficient enough to decrease lung volume
40
What is an open pneumothorax?
an unsealed opening in the chest wall impairing respiratory mechanisms => air moves in from atm
41
What is the atmospheric pressure value?
100kPa
42
What is the normal intrapleural pressure, relative to atmospheric pressure?
Intrapleural pressure is naturally sub-atmospheric ~99.5 kPa due to opposing elastic recoil of chest wall and lungs
43
What is the consequence of piercing either of the pleural membranes?
Will cause air to enter pleural cavity from either the lungs (closed) or the atmosphere (open) depending on the injury => pneumothorax
44
What is a closed pneumothorax?
When air / gas enters pleural cavity from lungs, without any external injury - normally occurs in CF / cancer patients (when lung already damaged)
45
What is the consequnece of pneumothorax?
Negative P(intrapleural) lost Chest wall and lungs no longer indirectly attached - will recoil in opposing directions causing lung tissue collapse => atelactasis
46
Describe the effect of entry of air into a pneumothorax
Increased pleural cavity volume at expense of lung volume (decreases) Reduces P(intrapleural) changes during inspiration - prevents proper lung expansion pneumothorax causes lung collapse - limits gas exchange
47
Outline how breathing occurs
1. Lung volume increases 2. Palv < Patm 3. air moves into lungs
48
Why is the difference in pressure between atm and alveoli not negated immediately ?
The difference in pressure aren't instantly negated as there's a delay due to the time taken for air to move
49
What is speed of airflow increased by?
- Decreased resistance - Increased Radius - Increased Pressure R ∝ 1/r⁴
50
How does air reach gas exchange surfaces?
To reach gas exchange structures, air must pass through a series of increasingly narrow and numerous airways
51
What causes impaired airway function?
Due to insufficient ventilation
52
What does rate of airflow depend upon?
The rate of airflow depends on the pressure gradients and level of airway resistance
53
Outline Ohm's Law
Airflow = ΔP / resistance ↑ΔP = ↑ airflow ↑ resistance = ↓airflow
54
Explain how a reduction in airway radius effects airflow
As airway radius decreases, Resistance increases, reducing airflow dramatically
55
What type of airflow increases resistance?
Turbulent flow
56
How does turbulent airflow increase airway resistance?
Air moves in different directions increasing resistance reducing speed of airflow
57
Describe the structure of alveoli in healthy individuals
Elastin in surrounding alveoli provides radial traction to splint bronchioles against positive Palv
58
How does COPD affect alveoli structure and airflow?
Without radial traction, bronchioles collapse causing obstruction
59
What causes a loss of airway patency in COPD?
Loss of airway patency due to degradation of structure causing airway obstruction Airways collapse due to lack of structural integrity
60
How can we calculate the total % of lung capacity an individual can exhale in the first second?
100 x FEV₁ / FVC = % FEV₁ - Forced expiratory volume (in 1 sec) FVC - Forced vital capacity (<80% is indicative of obstructive airways disease)
61
Describe the results for a patient with obstructive COPD
FEV₁ / FVC < 70% e. g. asthma - increased resistance
62
What would the results of a patient with restrictive COPD look like?
FEV₁ / FVC > 70% FVC < 80% e.g. Fibrosis - decreased compliance
63
Outline how you'd calculate Transpulmonary pressure Pₜₚ
Pₜₚ = Pₐₗᵥ - Pᵢₚ
64
What is transpulmonary pressure?
The level of force acting to expand the lung
65
What is lung compliance?
Lung compliance is the relationship between transpulmonary pressure and lung volume (higher lung CL, steeper gradient)
66
How does scoliosis muscular dystrophy + obesity affect lung CL?
Decreases lung compliance interfering with chest wall mechanisms
67
How does NRDS (newborn respiratory distress syndrome) affect compliance?
Affects alveolar surface tension - decreasing CL
68
What is the effect of fibrosis and COPD on lung compliance?
Affect the elastin fibres: - Fibrosis : ↓CL due to collagen deposition - COPD: ↑CL due to elastin degradation
69
How does emphysema affect lung compliance?
↑CL due to elastin degradation
70
How do air liquid interfaces resist inflation?
Generate surface tension which resist inflation
71
Give examples of air liquid interfaces
Alveoli are lined with fluid to enable gas exchange - the gas molecules dissolve into the water before diffusing.
72
Why does tension arise within the bubble formed by water-air interfaces?
Tension arises due to H-bonds between water molecules exerting a collapsing force towards the centre of the bubble
73
How does Laplace's law relate to the respiratory system?
Describes the pressure generated by surface tension within a bubble - collapsing force generates pressure, the amount within a specific bubble is described by Laplace's
74
Outline the equation used by Laplace's Law to calculate pressure generated
P = 2T/r p - pressure 2T - surface tension r - bubble radius (alveoli)
75
How does the size of alveoli affect the pressure generated at air liquid interfaces?
if T remains constant, P ∝ 1/r - smaller the alveoli, the larger the pressure generated
76
How is alveolar surface tension reduced?
Reduced by the presence of pulmonary surfactant, secreted by type II pneumocytes
77
What is the role of pulmonary surfactant?
Pulmonary surfactant act to equalise pressure and volume across varying alveoli
78
How does [surfactant] change as gas exchange occurs?
As alveoli expand, the [surfactant] decreases - increasing surface tension
79
How are the lungs kept inflated?
Larger alveoli tend to collapse into smaller ones, helping consistent inflation of the lungs
80
What role does pulmonary surfactant play in alveolar oedema?
Pulmonary surfactant help prevent alveolar oedema by reducing surface tension
81
How does surface tension affect alveolar oedema?
Surface tension produced at air-liquid interface also reduces hydrostatic pressure - fluid pulled out of surrounding capillaries -> alveoli
82
What is NRDS?
neonatal respiratory distress syndrome
83
What causes NRDS?
Insufficient surfactant production often due to: - premature birth - maternal diabetes - congenital development issues
84
Explain the effects of NRDS and how they occur
``` Premature birth / congenital defects ↓ Insufficient surfactant production ↓ Stiff (low CL), alveolar collapse, oedema ↓ Respiratory failure ↓ Pulmonary vasoconstriction, endothelial damage, acidosis, pulmonary & cerebral haemorrhage ```
85
How is NRDS treated?
- artificial surfactant supplementation | - maternal glucocorticoid supplementation

Respiratory System (10 decks)

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