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BS - Respiratory System > Development of the Lungs > Flashcards

Development of the Lungs Flashcards

1
Q

What structures make up the upper respiratory tract?

A

nasal cavitites

nasopharynx

oropharynx

larynx

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2
Q

Which structures make up the lower respiratory tract?

A 
trachea
bronchi
bronchioles
terminal bronchioles
respiratory bronchioles
alveolar ducts
alveolar sacs
alveoli
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3
Q

Which structures make up the conducting portion?

A 
nasal cavities
nasopharynx
oropharynx
larynx
trachea
bronchi
bronchioles
terminal bronchioles
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4
Q

Which structures make up the respiratory portion?

A

respiratory bronchioles
alveolar ducts
alveolar sacs
alveoli

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5
Q

Where is the first location where gas exchange can occur?

A

The respiratory bronchioles

This is not very efficient and is insufficient to sustain adult life

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6
Q

From which germ cell layers do the lungs develop?

A

The inner epithelial lining develops from the endoderm

The connective structures and vascular tissue are derived from the mesoderm

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7
Q

What is visible in a 4 week old embryo?

A

The yolk sac and somites are visible

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8
Q

What regions is the gut tube split into?

A
  1. foregut
  2. midgut
  3. hindgut
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9
Q

Where is the hindgut located?

A

It is anything below the Vitelline duct

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10
Q

What is the purpose of the Vitelline duct?

A

It connects the gut tube to the yolk sac

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11
Q

What is the respiratory diverticulum?

A

A growth from the gut tube which appears in the ventral wall of the foregut

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12
Q

When does the respiratory diverticulum start to develop?

A

It appears and starts to develop on day 22

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13
Q

In which direction does the respiratory diverticulum grow?

A

Ventrocaudally

forwards and towards the thoracic cavity

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14
Q

On day 22, how does the oesophagus exist and how is the respiratory diverticulum formed?

A

The developing oesophagus exists as just the gut tube

Ventral outpouching from the gut tube forms the respiratory diverticulum

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15
Q

How is the respiratory diverticulum separated from the foregut?

A

Tracheoesophageal ridges which eventually fuse to form a septum

The trachea then completely separates from the oesophagus

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16
Q

Where do the tracheoesophageal ridges not separate the respiratory diverticulum from the foregut?

A

At the laryngeal inlet

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17
Q

How does the respiratory diverticulum divide?

A

It will divide to form 2 lung buds

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18
Q

What is a fistula?

A

An abnormal connection

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19
Q

What is a tracheoesophageal fistula (TOF)?

A

An abnormal connection between the trachea and the oesophagus

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20
Q

How does a TOF arise?

A

An incomplete division of the foregut into oesophageal and respiratory portions

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21
Q

How often do TOFs occur?

A

In 1 in 3000-4500 live births

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22
Q

What is oesophageal atresia?

A

There is a fistula between the distal part of the oesophagus and the trachea

The proximal part of the oesophagus has failed to form completely leading to a blind-ended sac

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23
Q

What does atresia mean?

A

It describes the failure of a structure to form correctly

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24
Q

What is the “atresia” in oesophageal atresia?

A

The oesophagus is closed or absent

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25
Q

What % of TOFs show oesophageal atresia?

A

85 - 90%

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26
Q

What are the other 2 main types of TOF?

A

Oesophageal atresia without the abnormal connection between the oesophagus and trachea

There is no connection at all between the oesophagus and trachea

Fistula between the oesophagus and trachea without the oesophageal atresia

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27
Q

What % of TOFs show the other 2 main types?

A

Each type accounts for 4% of cases

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28
Q

What is the main symptom of oesophageal atresia associated with the fistula?

A

The abdomen rapidly distends as the stomach fills with air

The abnormal connection means some air enters the oesophagus which leads to the stomach

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29
Q

What is the main symptom of oesophageal atresia associated with the blind-ended sac?

A

The blind-ended sac will fill up until the contents of the food enter the respiratory system

No acid is produced in the lungs meaning there is a greater risk of infection

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30
Q

What is a H-type tracheoesophageal fistula?

A

A fistula that occurs between the trachea and oesophagus

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31
Q

What is the problem associated with a H-type TOF?

A

Milk is “driven” into the respiratory system

It enters the primary bronchi rather than following the oeosphagus into the stomach

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32
Q

What is meant by VACTERL or VATER associated abnormalities?

A

These describe a group of congenital malformations which often occur together

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33
Q

What does VACTERL stand for?

A

V - vertebral defects

A - anal atresia

(C) - cardiac defects

T - tracheoesophageal fistula

E - oesophageal atresia

R - renal abnormalities

(L) - limb defects

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34
Q

What happens around day 28 of development?

A

the respiratory diverticulum divides into the right and left primary bronchial buds

the oesophagus is partioned from the respiratory diverticulum

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35
Q

What happens during week 5 of development?

A

Further growth and development results in the formation of secondary (lobular) bronchial buds

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36
Q

How many lobular bronchial buds form?

Why?

A

3 form on the right side and 2 on the left

The presence of other cells around the bronchial buds determines the amount that will develop

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37
Q

What happens during the 6th week?

A

Tertiary (segmental) bronchial buds will form

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38
Q

Where are the segmental bronchial buds found and how many of them are there?

A

They will each supply a bronchopulmonary segment

There are 10 on the right and 8 on the left

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39
Q

When to terminal bronchioles form?

A

week 16

40
Q

When do respiratory bronchioles form?

Why is this significant?

A

week 26

No respiration can occur until these have formed

41
Q

When do the first alveoli develop?

A

week 36

42
Q

How is this process regulated?

A

The interaction of the epithelium with the overlying visceral mesoderm

The epithelium is derived from the foregut

43
Q

What structures will form from visceral mesoderm?

A

cartilage, smooth muscle, connective tissue and capillaries

44
Q

How does lateral plate mesoderm split?

A

Splits into visceral mesoderm and parietal mesoderm

45
Q

how are the pleura formed?

A

the visceral pleura forms from the visceral mesoderm

the parietal pleura forms from the parietal mesoderm

46
Q

What is pulmonary agenesis?

A

the failure of the lung bud to split leading to the complete absence of the bronchi and vasculature

47
Q

What is the difference between unilateral and bilateral pulmonary agenesis?

A

Unilateral is survivable as it is the failure to form one of the lungs

Bilateral is incompatible with life as both lungs have failed to form

48
Q

What is the clinical presentation of pulmonary agenesis in children?

A

They often develop respiratory distress which compromises lung function

If they acquire a LRT infection, the remaining lung is compromised

49
Q

What is cyanosis?

A

Occurs when a baby appears blue due to lack of oxygenation to their tissues

50
Q

How is pulmonary agenesis related to other congenital anomalies?

A

60% of children will have other congenital anomalies including cardiac lesions, diaphragmatic hernias and skeletal anomalies

Agenesis of the right lung is associated with higher frequency of anomalies

51
Q

What are the clinical presentations of pulmonary agenesis in adults?

A

Progressive breathlessness

Enlarged right lung and deviation of the heart and trachea into the empty space

52
Q

What is meant by hypoplasia?

A

It describes when a structure fails to develop to its normal size

53
Q

What is pulmonary hypoplasia?

A

All of the components of the lung are present, but they are incompletely developed

54
Q

What is pulmonary hypoplasia often found in association with?

A

Congenital diaphragmatic hernia (CDH)

55
Q

What is a CDH?

A

The diaphragm fails to form correctly

The intestines and other abdominal structures are pushed into the thoracic cavity

56
Q

How does CDH usually lead to pulmonary hypoplasia?

A

The lung does not have enough space to develop so ends up being smaller

57
Q

What happens if all of the abdominal contents develop in the thorax?

A

Death as there is not enough space for the heart or lungs to form

58
Q

What does a change in branching morphogenesis lead to?

A

Development of supernumerary lobes or segments

59
Q

What is the extra lobe that often forms?

A

An azygous lobe which forms due to the branching pattern of the bronchioles

60
Q

How does branching morphogenesis affect the function of the lungs?

A

It has no functional significance

61
Q

What are the 4 periods of lung maturation?

A
  1. pseudoglandular
  2. canalicular
  3. saccular/terminal sac
  4. alveolar
62
Q

What is significant about the maturation periods of the lungs?

A

They all overlap slightly

63
Q

When does the pseudoglandular period occur?

A

between 5 and 17 weeks

64
Q

What happens during the pseudoglandular period?

A

Branching of the respiratory tree to form terminal bronchioles

65
Q

Would a foetus in the pseudoglandular period survive?

A

No as respiratory bronchioles have not yet developed so respiration is not possible

66
Q

What other reasons mean respiration cannot occur during the pseudoglandular period?

A

The capillaries are not close enough to the epithelium for respiration to occur

The epithelium is not yet specialised for gas exhange

67
Q

When does the canalicular period occur?

A

between 16 and 25 weeks

68
Q

What happens during the canalicular period?

A

terminal bronchioles give rise to respiratory bronchioles, which give rise to alveolar ducts

mesodermal tissue becomes highly vascularised and the capillaries are moving closer to the epithelium

69
Q

Could a foetus survive during the canalicular period?

A

There is a low chance of survival

respiration is possible towards the end of this period as some terminal sacs have developed at the ends of respiratory bronchioles

70
Q

What is the % chance of survival during the canalicular period?

A

18-20 weeks - 2% chance

25 weeks - 60% chance

71
Q

When does the terminal sac period occur?

A

from 26 weeks until birth

72
Q

What happens during the terminal sac period relating to the epithelium?

A

The epithelium thins and the capillaries come into close contact with it

This allows for efficient gas exchange as the diffusion distance is short

73
Q

What is the main thing that happens during the terminal sac period?

A

Further terminal sacs develop

these are primitive alveoli

74
Q

What forms during the terminal sac period?

A

The blood-air barrier

75
Q

What cells are formed from differentiation of the epithelium during the terminal sac period?

A
  1. type I pneumocytes which allow gas exchange to occur

2. type II pneumocytes which secrete surfactant

76
Q

What is the role of surfactant?

A

It forms a film over the internal walls of terminal sacs to decrease the surface tension inside the terminal sac

This facilitates inflation

77
Q

How does surfactant lead to more efficient gas exchange?

A

It allows for inflation of both the small and large alveoli

This leads to more efficient filling of the alveolar sacs and more efficient gas exchange

78
Q

Could a foetus born during the terminal sac period survive?

A

If they are born prematurely (24 weeks) they can survive with intensive care

But they may suffer from respiratory distress syndrome

79
Q

When does the alveolar period occur?

A

from 36 weeks until 8 years of age

80
Q

What happens during the alveolar period?

A

Increase in the number of respiratory bronchioles and alveoli

More alveoli are developing but they are NOT increasing in size

81
Q

What % of mature alveoli develop after birth?

A

95%

82
Q

When do breathing movements start in the foetus and why?

A

They start in utero and serve to remove amniotic fluid

This starts to tone the respiratory muscles

83
Q

What happens to remaining amniotic fluid at birth?

A

The baby coughs up amniotic fluid and any remaining lung fluid is reabsorbed into the capillaries

84
Q

What determines whether respiration is possible at birth?

A

Surfactant must be present in sufficient amounts

85
Q

What circulatory changes take place at birth and why?

A

The direction of blood flow is changed

This allows gas exchange to occur at the lungs as oxygenated blood no longer comes from the mother

86
Q

What is the main factor that determines whether a premature child will survive?

A

Whether surfactant has been produced in sufficient quantities

(after 26 weeks survival is likely)

87
Q

What happens if not enough surfactant has been produced?

A

Collapsed alveolar sacs

88
Q

When does respiratory distress syndrome occur (RDS)?

A

When a baby is born prematurely

89
Q

What happens in RDS?

A

Laboured breathing threatens the infant with immediate asphyxiation

90
Q

How is breathing supported in RDS?

A

There is an increased rate of breathing and mechanical ventilation is often needed to support breathing

91
Q

What happens to the alveoli in RDS?

A

The alveolar lining is damaged due to fluid and serum proteins leaking into the alveolus

Continued injury may lead to detachment of the alveolar lining

92
Q

What can chronic lung injury in preterm infants lead to?

A

Bronchopulmonary dysplasia

Damage to the lungs caused by mechanical ventilation

93
Q

What is the treatment for RDS if the mother is susceptible to pre-term birth?

A

Glucocorticoid treatment

Involves administering steroids to the mother

94
Q

What does glucocorticoid treatment do?

A

It accelerates foetal lung development and surfactant production

95
Q

What is the treatment for RDS after birth?

A

Surfactant therapy - administering natural or artificial surfactants

More effective with surfactant A and B

96
Q

What are the roles of surfactant A and B?

A

A - present where gas exchange occurs

B - involved in organisation of other surfactants

97
Q

Why is Surfactant Protein B deficiency disease fatal?

A

Therapy is not sustainable as the surfactant will never be produced throughout life

BS - Respiratory System (20 decks)

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