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Respiratory > Lecture 3- Mechanics underlying ventilation of the lungs > Flashcards

Lecture 3- Mechanics underlying ventilation of the lungs Flashcards

1
Q

ventilation is the process of

A

inspiration and expiration/ physical action of breathing and moving air into and out of the lung/ movement of a volume of gas into and out of the lungs

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2
Q

respiration is the process of

A

oxygen and CO2 exchange across a membrane in the lungs at a cellular layer

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3
Q

normal tidal volume in quiet inspiration and expir

A

400-500ml

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4
Q

Quite inspiration and expiration is a

A

rhythmic and involuntary process - neurones in resp centre of brain automatically generate impulses to inspiratory muscles

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5
Q

what underlies why we are able to breath

A

due to Boyles law

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6
Q

boyles law shows

A

Inverse relationship between the volume that a gas occupies and the pressure exerted on that gas

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7
Q

Gas contained in a smaller volume=

A

higher pressure

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8
Q

Gas contained in a larger volume=

A

lower pressure

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9
Q

lung mechanics in quiet inspiration

A
  • Requires active expansion of the thoracic cavity - which in turn expands the lungs – increase in volume causes decrease in pressure relative to atmosphere - Air is drawn into the airways
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10
Q

outline the lung mechanics in quiet expiration

A
  • Air expelled from the airways passively, by relaxing muscles used in inspiration reduces volume of thoracic cavity - reduces volume of lungs - this increases pressure inside lungs relative to atmosphere and air expelled
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11
Q

Lungs have a natural

A

elastic recoil - Tendency to want to collapse into o Especially with increased stretch o Yet lungs are kept against chest wall within physical attachment during inspiration and expiration

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12
Q

What keeps the lungs against the chest

A
  • PLEURAL FLUID is found between visceral and parietal pleura (in intrapleural spcace) forms seal between lungs and thoracic wall because of surface tension o So lungs expand with the thoracic cavity
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13
Q

the pleural seal

A

Surface tension between the pleural surfaces created by the presence of thin film of pleural fluid holds outer surface of lung (base of my cup/bottle) to inner surface of chest

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14
Q

Summary of pressure changes and air movement Inspiration

A
  • expansion of thoracic cavity and lungs – ↑volume and ↓pressure (relative to atmospheric pressure) – Moves air into airways (lung) – Active requiring contraction of external intercostals and diaphragm (80%)
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15
Q

Summary of pressure changes and air movement expiration

A

– reducing size of thoracic cavity and lungs – ↓ volume and ↑ pressure (relative to atmospheric pressure) – Moves air out of airways (lung)

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16
Q

intrapleural sapce

A

space between pleuras

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17
Q

pressure in the intrapleural space

A

negative (relative to atmospheric pressure)

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18
Q

why is the intrapleural space negative

A

due to recoil of lung pulling visceral pleura inwards and the chest wall pulling parietal pleura outwards - Intrapleural pressure is negative throughout expiration and inspiration (becomes more negative up until end of inspiration

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19
Q

what holds the visceral and parietal pleura together

A

the pleural seal

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20
Q

What would happen if the pleural seal were broken?

A
  • The lungs would collapse- pneumothorax
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21
Q

What do we call the state when we have just expired and before we start inspiring?

A
  • Resting expiratory level (during quite breathing)- represents a physiological state
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22
Q

Resting expiratory level represents

A

o Represents equilibrium (balance) between elastic recoil chest outwards and elastic recoil inwards

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23
Q

resting expiratory level is not a

A

volume

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24
Q

the volume of air during resting expiraotry level (REL)=

A

functional residual capacity (FRC)

25
Q

during REL (the state of equilibirum) what is happening to the lungs and the chest wall

A
  • Lungs collapse inwards (lung elastic recoil) - Chest wall pulls out (chest elastic recoil) o Forces are equal and opposite so balance out (no movement of chest wall) - Tendency to always want to return to this resting state
26
Q

ventilation disturbs REL… inspiration

A
  1. Inspiration is active a. Muscles contract to allow the chest wall and diaphragm to overcome inward pull of the lung recoil
27
Q

inspiration is an

A

active process

28
Q

Expiration is

A

passive

29
Q

ventilation disturbs this equilibrium… expiration

A

a. Muscles stop contracting b. Chest wall and diaphragm no longer overcome inward pull of lung recoil c. Return to REL

30
Q

forced ins and ex uses

A

lung reserve volumes but requires more effort

31
Q

difference b/w quiet and forced ventilation

A
  • Going beyond quiet inspiration and expiration - Used during exercise but also when diseases affect the lungs - Required involvement of more muscles
32
Q

name four accessory muscles of inspiration

A

Sternocleidomastoid Scalene muscles Serratus anterior Pectoralis major

33
Q

name two accessory muscles of expiration

A

internal intercostals abdominal wall muscles

34
Q

forced expiration is an……. process compared to being an ….. process during quiet ventilation

A

active passive

35
Q

tidal volume

A

represents the volume of air entering and leaving the lungs in a single breath (during quiet inspiration and expiration) (400-500ml)

36
Q

Inspiratory reserve volume-

A

air breathed in above a quiet inspiration during exercise

37
Q

Expiratory reserve volume-

A

extra air that can be forced out of lungs after normal breath

38
Q

Residual volume-

A

the air left in the lungs after the expiratory reserve volume (to keep alveoli open) (cannot be measured by spirometer)

39
Q

Functional residual capacity-

A

amount of air left in the lungs after a quiet expiration (at resting respiratory level- functional residual capacity)

40
Q

Inspiratory capacity-

A

the amount you take in on a normal breath + the amount above and beyond you can take in

41
Q

Vital capacity-

A

the amount of air that we can expire after a maximal inspiration

42
Q

Forced vital capacity-

A

the amount of air that can be expired when forced

43
Q

why is the alveoli surface lined by fluid

A
  • Creates surface tension that limits their expansion
  • Decreases compliance making it difficult for alveolar (and therefore lungs) to expand
44
Q

what counters the surface tension created by fluid which lines alveoli

A

surfactant

45
Q

surfactant produced by

A

type II pneumocytes in lungs

46
Q

surfactant has what properties

A

detergent- o Acts to disrupt interaction between fluid molecules on alveolus surface.. reducing surface tension

47
Q

to summarise surfactant..

A

o Acts to disrupt interaction between fluid molecules on alveolus surface.. reducing surface tension

48
Q

surfactant is more effective at disrupting surface tension when its

A

molecules are closer together i.e. around smaller alveoli

49
Q

smaller alveoli have surfactant molecules which are

A

close together  More effective at disrupting surface tension of fluid  Reduced surface tension  Reducing surface tension in smaller alveoli prevents pressure rising (within the alveolus) as a result of the smaller volume

50
Q

reducing surface tension (by having surfactant which is closer together) in smaller alveoli…

A

prevents pressure rising (within alveolus) as a result of the smaller violume

51
Q

larger alveoli surfactant molecules spread

A

further apart - less effective at disturbing the surface tension

52
Q

surface tension increase as

A

alveoli increase in size i.e. as lungs expand (hence forced inspiration harder than quiet inspiration)

53
Q

Due to surfactant, surface tension in larger alveoli

A

>>smaller alveoli – effectively surfactant ‘diluted’ in larger alveoli

54
Q

Due to surfactant, surface tension in larger alveoli >>smaller alveoli – effectively surfactant ‘diluted’ in larger alveoli thus….

A

pressure inside the bigger alveoli stays high despite it being bigger

55
Q

surfactant ensures pressure sin alveoli does not drop despite increase in size

A

• i.e. pressure does not drop despite increased ‘volume’ of the alveolus, as the increased pull ‘inwards’ from the surface tension counters this • If pressure remains high in bigger alveoli, keeps pressures equal to smaller alveoli • Prevents collapsing of small alveoli into big alveoli

56
Q

Ventilate the lungs to allow for gaseous exchange at the alveoli

A
  • Air moves through a series of airways to reach alveoli - Need to overcome resistance to flow - Tubes of smaller diameter have higher resistance to flow (Poiseuilles law) o Many airways in the lungs are small o Individual resistance is high
57
Q

what compensates for the small airways with higher resistance to flow

A

Parallel arrangement of small airways compensates for increase in their individual resistance Over whole expanse of airways • Numerous airways running in parallel • Compensates for increase in their ‘individual’ resistance

58
Q

Summary (to read)

A

• Ventilation is the movement of air into and out of our lungs • Governed by lung and thoracic cavity mechanical properties and forces • (Quiet) Inspiration active process – Boyle’s Law- increase volume, decrease pressure, intrapulmonary pressure < atmospheric and air travels inwards • (Quiet) Expiration passive process – Boyle’s law - decrease volume, increase pressure, intrapulmonary pressure >atmospheric and air travels outwards • Pleural seal connects visceral and parietal pleura so that when chest cavity expands so do lungs • Surfactant lowers alveolar surface tension – diluted in larger alveoli so that even though they are bigger Boyle’s law partially countered- keeps smaller alveoli inflated • Ventilation has to overcome airways resistance – numerous small airways running in parallel creates effective massive diameter and hence low resistance

Respiratory (27 decks)

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