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Second Year - Biomedical Sciences BS22001 > Lecture 22 - Lung Development, Structure And Gas Movement > Flashcards

Lecture 22 - Lung Development, Structure And Gas Movement Flashcards

1
Q

What are the five phases of lung development

A 
Phase 1 - Embryonic
Phase 2 - Pseudoglandular
Phase 3 - Canalicular
Phase 4 - Saccular
Phase 5 - Alveolar
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2
Q

What doe the five phases of lung development lead to

A

The formation of the alveolar blood-gas barrier

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3
Q

What is established during phase 1

A

The basic lung structure as a template for further growth

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4
Q

When does the formation of the right and left lobes occur

A

Between 26 days and 6 weeks

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5
Q

What does the primordial lung develop as

A

Buds which extend outwards from the foetal foregut

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6
Q

What is established in phase 2

A

The branched network of gas conducting airways

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7
Q

When does phase 2 occur

A

Between weeks 6-16 of gestation

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8
Q

What creates a distending pressure

A

Fluid secretion into the airway

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9
Q

What does the distending pressure give

A

Mechanical support for the growth of the airway in three dimensions

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10
Q

At the end of phase 2 what has happened to the airways and vasculature

A

They have developed to completely fill the space available in the chest cavity

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11
Q

What is the developmental outcome of phase 2

A

The formation of the conducting airways of the lungs and accompanying blood vessel

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12
Q

What is the airways and accompanying blood vessels of the lung known as collectively

A

The respiratory tree

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13
Q

What type of branching does the airway of the lung follow

A

Irregular dichotomous branching

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14
Q

What are the advantages of irregular dichotomous branching

A

It achieves even dispersion of gas among terminal airways branches and the mechanical strain is dispersed evenly among units

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15
Q

What does the regulated increase of the number of airways at each branch allow

A

The dispersion of airflow resistance

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16
Q

What drives fluid movement into the airway lumen

A

A chloride gradient

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17
Q

What happens in phase 3

A

The airways and blood vessels meet to form an interface known as the blood-gas barrier

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18
Q

When does phase 3 occur

A

Between weeks 16-24 of gestation

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19
Q

What is the onset of phase 3 marked by

A

The extensive angiogenesis within the mesenchyme that surround the more distal reaches of the embryonic respiratory system which forms dense capillary network

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20
Q

The increase of the diameter of the air is accompanied by

A

A decrease in epithelial thickness to a more cuboidal structure

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21
Q

When does epithelial cell differentiation occur

A

Canalicular phase (phase 3)

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22
Q

What does differentiation of the mesenchyme progressing down the developing respiratory tree give rise to

A

Chondrocytes, fibroblasts and myocytes

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23
Q

What is the earliest stage of lung development that a premature baby could survive at

A

Canalicular (phase 3)

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24
Q

During phase 4 the first what occurs

A

The first septal fold of the early alveolus occurs

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25
Q

What does phase 4 define

A

The gas exchange zone of the lungs

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26
Q

What is the gas exchange zone of the lungs known as

A

The respiratory acinus

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27
Q

When does phase 4 occur

A

Between weeks 24-36 of gestation

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28
Q

What happens during phase 4

A

The branching and growth of the terminal sacs or primitive alveolar ducts and continued thinning of the storm bringing the capillaries into apposition with the prospective alveoli

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29
Q

The completion of what differentiation occurs during phase 4

A

The pneumocyte differentation

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30
Q

What do type I pneumocytes differentiate from

A

Cells with type-II like phenotypes

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31
Q

What happens to type I pneumocytes

A

They flatten, increasing the epithelial surface area by dilation of the saccules

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32
Q

The production of what is fully functional in phase 4

A

Surfactant

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33
Q

What has formed by 26 weeks

A

A rudimentary though functional blood-gas barrier

34
Q

Through what process does further maturation the alveoli occur

A

Further enlargement of the terminal sacs, deposition of elastic foci and development of vascularised septae around the foci

35
Q

What continues to thin to allow the capillaries to protrude into the alveoli

A

The stroma

36
Q

When the septa forms what happens

A

Bifurcation of the airway terminus

37
Q

What does the septum contain

A

Two closely apposed capillary networks

38
Q

What is the patency of the thin-wall airway maintained by

A

Cl- driven secretion into the luminal space

39
Q

What happens during phase 5

A

The gas exchange surface area is increased

40
Q

When does phase 5 occur

A

36 weeks to 6 years

41
Q

What clears the lungs of fluid

A

Na+ driven fluid adsorption in the lung lumen

42
Q

When does pulmonary circulation become fully established

A

When the umbilical cord is cut off

43
Q

How does enlargement of the gas exchange surface occur

A

By pocketing on the wall of the saccular lung

44
Q

What are the basic anatomical features of the lungs

A

The trachea, pleura, bronchi and alveoli

45
Q

Where does the trachea run from/to

A

It runs from below the larynx (C6/7) to the carina

46
Q

What is the trachea composed of

A

C-shaped cartilage and small muscles that connect the cartilage

47
Q

Which direction do the C-shaped cartilage face

A

Anteriorly

48
Q

When the trachea bifurcates what does it give

A

The left and right main bronchi

49
Q

What is the main function of the lungs

A

To oxygenate the blood

50
Q

What does the parietal pleura line

A

The pulmonary cavity

51
Q

What are the different parts of the parietal pleura

A

Cervical, costal, diaphragmatic and mediastinal

52
Q

What is the pleura that covers the lungs

A

Visceral pleura

53
Q

What is the name for the sleeve of pleura that hangs from the lung root

A

The pulmonary ligamnet

54
Q

What do the main bronchi go onto form

A

Lober bronchi

55
Q

What do lober bronchi go onto form

A

Segmental bronchi

56
Q

How many lober bronchi are in the left lung

A

Two

57
Q

How many lober bronchi are in the right lung

A

Three

58
Q

What are attached to the bronchi

A

Alveoli

59
Q

What are the respiratory surfaces within the lung

A

The alveoli

60
Q

What are alveoli

A

Air-filled spaces that are closely associated with capillaries within the lungs

61
Q

What type of gradient does gas follow

A

A partial pressure gradient

62
Q

What does partial pressure tell you

A

The direction of movement of gas

63
Q

What is the ENaC

A

A Na+ selective ion channel

64
Q

Where is ENaC found

A

In all secretory epithelia

65
Q

What increases during the third trimester of pregnancy

A

The maternal cortisol levels

66
Q

What happens when cortisol enters the foetal circulation

A

It induces the ENaC subunit gene expression and membrane insertion in epithelial cells lining the foetal airways

67
Q

During labor what activates the ENaC

A

The rise in the level of adrenaline within the mum which passes into foetal circulation

68
Q

What does the ENaC channel allow for

A

Fluid to be rapidly cleared from the foetal lung in preparation for the first breath

69
Q

What are the two advantages of airway branching

A

It causes an increase in the surface area for gas exchange and dissipates resistance to air flow as airway diameter narrows towards the respiratory zone

70
Q

What drives the bulk of gas into the conductive zone

A

Net pressure caused by expansion and relaxation of the chest cavity

71
Q

When will gas move into the alveoli

A

When the alveolar pressure is less than the atmospheric pressure and the airway is open

72
Q

How does gas movement in the airways arise

A

By convection

73
Q

When will gas move out of the alvoli

A

When the alveolar pressure is greater than the atmospheric pressure and the airway is open

74
Q

What is alveolar pressure the sum of

A

Elastic recoil pressure and pleural pressure

75
Q

What muscles are involved in inspiration

A

The diaphragm, external intercostal and the accessory muscles

76
Q

What nerves control the diaphragm

A

The phrenic nerves

77
Q

What happens to the diaphragm during inspiration

A

It flattens on contraction

78
Q

What are external intercostal muscles innervated by

A

The intercostal nerves

79
Q

What are the accessory muscles

A

The sternomastoid, scalenes anterior, medius and posterior, and the pectoralis major and minor

80
Q

What happens to the intrapleural pressure as the chest expands

A

It falls

81
Q

What muscle are involved during forced expiration

A

The internal intercostal muscles

Second Year - Biomedical Sciences BS22001 (28 decks)

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