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Respiratory strand: Lecture 7 - Development of Lungs Flashcards

1
Q

How is the respiratory tract divided anatomically?

A
  • Upper respiratory tract

- Lower respiratory tract

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2
Q

What does the upper respiratory tract consist of?

A
  • nasal cavities
  • nasopharynx
  • oropharynx
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3
Q

What does the lower respiratory tract consist of?

A

-trachea
-bronchi
-bronchioles
-terminal bronchioles
-respiratory bronchioles
-alveolar ducts
-alveolar sacs
-alveoli
diagram slide 3

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4
Q

What structure divides the URT from the LRT?

A

The larynx

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5
Q

What are the 3 germ layers?

A

ectoderm
mesoderm
endoderm

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6
Q

Which germ layer does the inner epithelial lining come from?

A

endoderm

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7
Q

Which germ layer does the connective structures like blood vessels come from?

A

mesoderm

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8
Q

Give 5 developments of the embryo by week 4?

A
  • yolk sac visible
  • somites visible
  • CNS development
  • gut tube formed
  • respiratory diverticulum (lung bud) appears in ventral wall of foregut
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9
Q

How is the gut tube divided?

A

-foregut (area above septum transverse)
-midgut (yolk sak)
-hindgut (anything distal/below yolk sak)
image slide 5

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10
Q

What occurs in the gut tube?

A

Its where we develop our respiratory system via the respiratory diverticulum

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11
Q

What occurs on day 22?

A

Lung bud forms

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12
Q

In which direction does the lung bud grow?

A

ventrocaudally

front and tail ways

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13
Q

What separates the respiratory diverticulum from the foregut?

A

tracheoesophageal ridges

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14
Q

What is happening in this image?

slide 6

A
  • ventrally, trachea and lung bud divide to form two lung buds
  • yellow and blue tube separate to form oesophagus and trachea
  • separate trachea and oesophagus then a trachea septum
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15
Q

What is a fistula?

A

An abnormal communication/ connection

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16
Q

What is a TOF?

A

Tracheoesophageal fistula -

abnormal connection between trachea and oesophagus

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17
Q

Why might a TOF occur?

A

from incomplete division of the foregut into oesophageal ad respiratory portions

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18
Q

What is oesophageal atresia?

A

slide 7 configuration A

  • closed or absent oesophagus
  • distal part of oesophagus still connected to trachea - narrowed so much it closes
  • upper oesophagus ends abruptly; lower oesophagus forms fistula with trachea
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19
Q

What is the effect of a Tracheoesophageal Fistula with Oesophageal Atresia?

A
  • abdomen rapidly distends as stomach fills with air (air goes down trachea and escapes into oesophagus and then stomach)
  • stomach contents can make way up to the respiratory system from the oesophagus
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20
Q

What is an H type tracheoesophageal fistula?

A

-much more rare than TOF
-isolated fistula
-milk may be ‘driven’ into respiratory system
slide 9

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21
Q

What does the VACTERL or VATER acronym stand for? why is it important?

A 
V-  Vertebral defects 
A- Anal atresia 
(C)- Cardiac defects
T - Tracheo-oesophageal fistulas 
E- Esophageal atresia 
R - Renal abnormalities 
(L) - Limb defects 
TOF's are usually associated with other congenital abnormalities - most commonly cardiac defects
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22
Q

What happens during partitioning of oesophagus and respiratory diverticulum?

A

Right and left lung buds form

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23
Q

What happens during week 5?

A
  • further growth and differentiation results in formation of main bronchi
  • main bronchi form secondary bronchi (3 right, 2 left)
24
Q

What happens during week 6?

A

-further branches results in the formation of the tertiary bronchi - these will each supply a bronchopulmonary segment / bronchial tree (10 right, 8 left)
image slide 11

25
What happens by week 16?
branching continues to form terminal bronchioles
26
What happens by week 26?
- forms respiratory bronchioles | - gaseous exchange can occur (although inefficient)
27
What happens by week 36?
first alveoli develop
28
How is branching regulated?
-By the interaction of the epithelium (derived from the foregut) with the overlying visceral mesoderm
29
What do the cartilage, smooth muscle, connective tissue and capillaries form from?
Formed from visceral mesoderm
30
Which germ layer forms the pleura?
Mesoderm
31
How do we ensure the branching pattern is correct?
Its regulated by the mesoderm and endoderm - they send signals and communicate with each other to stimulate the correct branching pattern
32
What does the mesoderm split into?
The visceral mesoderm and parietal mesoderm
33
What does the visceral mesoderm form?
The visceral pleura
34
What does the parietal mesoderm form?
The parietal pleura
35
What is pulmonary agenesis?
- Failure to form a lung | - complete absence of bronchi and vasculature
36
When does this occur?
When a lung bud fails to split
37
What are the two types of pulmonary agenesis? | which is the most severe?
unilateral or bilateral | bilateral genesis is incompatible with life
38
What is the clinical presentation of unilateral pulmonary agenesis?
- child usually develops respiratory distress - remaining lung is compromised, usually by LRT infection - 60% have other congenital anomalies including cardiac lesions, diaphragmatic hernias, and skeletal abnormalities - agenesis of the right lung is associate
39
If you have left agenesis, what will your right lung look like?
it will be enlarged as its compensating
40
What is pulmonary hypoplasia?
- all components are developed, but incompletely developed - severity of hypoplasia determines the degree of respiratory compromise - may be found in association with congenital diaphragmatic hernia (CDH)
41
Whats the definition of hypoplasia?
Fails to form fully
42
What is branching morphogenesis?
- Supernumerary lobes and segments - when branching pattern goes wrong - little functional significance
43
Explain the 4 periods of maturation of the lung?
1. Pseudoglandular 2. Canalicular 3. Saccular/ terminal sac 4. Alveolar image slide 17 - little overlap between each process
44
When is the pseudo glandular period?
5-17 weeks
45
What occurs in the pseudo glandular period?
- branching of the respiratory tree has occurred to form terminal bronchioles - respiration is NOT possible; therefore foetus could not survive
46
When is the canalicular period?
16-25 weeks
47
What occurs during the canalicular period?
- terminal bronchioles give rise to respiratory bronchioles, which give rise to alveolar ducts - mesodermal tissue becomes highly vascularised - respiration is possible towards end of canalicular period as some terminal sacs have developed at the ends of the respiratory bronchioles - inefficient gaseous exchange can occur: better prognosis for birth at this point
48
When is the terminal sac period?
26 weeks - birth
49
What occurs during the terminal sac period?
- further terminal sacs (primitive alveoli) develop - epithelium thins and capillaries come into 'contact' with epithelium - blood-air barrier formed - surfactant forms a film over the internal walls of terminal sacs - decreases surface tension thus facilitating inflation - foetus born prematurely (24 weeks) can survive if given intensive care but may suffer from respiratory distress
50
What does surfactant do?
Prevents alveoli from collapsing when theres low pressure
51
When is the alveolar period? (where we develop alveolar sacs)
36 weeks- 8 years | -95% of mature alveoli do not develop after birth
52
Why do the lungs develop mostly after birth?
Due mainly to an increase in the number of respiratory bronchioles and alveoli
53
When do breathing movements start?
in utero | this serves to remove amniotic fluid (we inspire it)
54
What happens to any remaining lung fluid at birth?
Its reabsorbed by capillaries
55
Why do you have a good chance of survival if you're born from 26 weeks onwards?
Surfactant is produced in sufficient qualities
56
What will occur for a birth at 23 weeks?
- laboured breathing - increased rate of breathing - mechanical ventilation needed - damage to alveolar lining; fluid and serum proteins leak into alveolus - bronchopulmonary dysplasia (abnormal formation)
57
What does glucocorticoid treatment do?
Accelerates fatal lung development and surfactant production this must be taken before birth to increase surfactant

Body Systems (24 decks)

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