Respiratory embryology

Question 1

Where does the upper respiratory tract run from?

Answer 1

The nasal cavities to the oropharynx

Question 2

Where does the lower respiratory tract run from?

Answer 2

The larynx to the alveoli

Question 3

Where does the conducting portion of the respiratory tract run from?

Answer 3

The nasal cavities to the terminal bronchioles

Question 4

Where does the respiratory portion of the respiratory tract run from?

Answer 4

The respiratory bronchioles to the alveoli

Question 5

What germ layer is the respiratory tract derived from?

Answer 5

Respiratory epithelium from the endoderm

The supporting structures ie. musculature, cartilage and vasculature all derived from the mesoderm

Question 6

Where does the respiratory diverticulum/lung bud appear from?

Answer 6

The ventral wall of the foregut

Question 7

On what day does the lung bud appear?

Answer 7

Day 22

Question 8

What separates the respiratory diverticulum from the foregut?

Answer 8

The tracheoesophageal ridges

Question 9

In how many cases are tracheosophageal fistulas associated with oesophageal atresia?

Answer 9

85-90%

Question 10

What are the signs of tracheoosophageal fistula with oesophageal atresia in the newborn?

Answer 10

Distended abdomen (swallows air)
Regurgitation of milk
lung infection as stomach contents can enter the lungs

Question 11

What is a H type tracheosophageal fistula?

Answer 11

No oesophageal atresia but a connection between oesophagus and trachea
Occurs is approximately 4 % of cases
Similar symptoms to that with oesophageal atresia but can still swallow

Question 12

What other congenital abnormality are tracheoesophageal fistulas commonly associated with?

Answer 12

Cardiac defects

Question 13

What are the VACTERL commonly associated congenital abnormalities?

Answer 13

V = vertebral defects
A = anal atresia
C = cardiac defects
T = TOFs
E = Esophageal atresia
R = Renal abnormalities
L = limb defects

Question 14

How many secondary bronchi do you have on the right and left and during which week do they form?

Answer 14

Week 5
3 on right
2 on left
One to each lobe

Question 15

How many tertiary bronchi do you have on the right and left and in which week do they develop?

Answer 15

Week 6
10 on right
8 on left
Each supply a bronchopulmonary segment

Question 16

In which weeks do the terminal bronchioles, respiratory bronchioles and alveoli develop?

Answer 16

Terminal bronchioles = by Week 16
Respiratory bronchioles = by Week 26
First alveoli develop in week 36

Question 17

What is the branching of the respiratory tract during development regulated by?

Answer 17

Interaction between the respiratory epithelium (Derived from the foregut) with the overlying visceral mesoderm

Question 18

What part of the lungs is derived from the visceral mesoderm?

Answer 18

Cartilage, smooth muscle, connective tissues and capillaries

Question 19

What forms the visceral and parietal pleura of the lungs?

Answer 19

Visceral pleura = visceral mesoderm

Parietal pleura = parietal mesoderm

Question 20

What is pulmonary agenesis and what are the 2 types?

Answer 20

Occurs when lung bud fails to split
Complete absence of bronchi and vasculature
Can be unilateral or bilateral
Bilateral agenesis is incompatible with life

Question 21

What is pulmonary hypoplasia and how severe is it?

Answer 21

All components of the lung are present but are incompletely developed
Severity of hypoplasia determines the degree of compromise

Question 22

What other congenital defect is pulmonary hypoplasia commonly associated with?

Answer 22

Congenital diaphragmatic hernia

Question 23

What is branching morphogenesis and how does this affect function?

Answer 23

Supernumerary lobes or segments

Little functional significance

Question 24

What 4 sections can maturation of the lungs be divided into?

Answer 24

1) Pseudoglandular
2) Canalicular
3) Terminal Sac
4) Alveolar

Question 25

What weeks is the pseudoglandular period from, how far does the respiratory system develop in this period and is respiration possible?

Answer 25

5-17 weeks
Terminal bronchioles have formed
Respiration not possible - fetus could not survive

Question 26

What is the canalicular period from, how has the structure of the respiratory tract developed and is respiration possible?

Answer 26

16-25 weeks
Terminal bronchioles give rise to respiratory bronchioles which give rise to alveolar ducts, mesoderm also becomes highly vascularised
Respiration is possible towards the end of this period but low chance of survival

Question 27

When is the terminal sac period from, what structural changes occur to the lungs?

Answer 27

17 weeks to birth
Further terminal sacs (primitive alveoli develop) Epithelium thins and comes into contact with capillaries, blood air barrier forms
respiratory epithelium divides into type 1 and type 2 pneumocytes which produce surfactant

Question 28

Can a fetus born prematurely survive?

Answer 28

Yes (24 weeks) if given intensive care but may suffer from respiratory distress syndrome

Question 29

When is the alveolar period from, what kind of development happens during this period?

Answer 29

36 weeks - 8 years

Development mainly due to increase in the number of respiratory bronchioles and and alveoli

Question 30

What percentage of mature alveoli develop after birth?

Answer 30

95%

Question 31

When does breathing movements begin and why?

Answer 31

Starts in utero and serves to remove amniotic fluid and also kick starts muscles of respiration into action

Question 32

What happens to the fluid the lungs and what does the babies first breath cause?

Answer 32

Any remaining fluid in the lungs is reabsorbed by the capillaries
The first breath causes circulatory changes

Question 33

What is usually the prime factor in a babies survival if born prematurely?

Answer 33

The state of development of the lungs - the presence of the respiratory portion of the system but also alveoli

Question 34

Why does respiratory distress syndrome occur?

Answer 34

Absence of surfactant

Question 35

What happens in respiratory distress syndrome?

Answer 35

Laboured breathing as it threatens the infant with asphyxiation
Increased breathing rate

Question 36

What is needed to support the babies breathing in respiratory distress syndrome but what can this cause?

Answer 36

Mechanical ventilation
Damage to the alveolar lining , fluid and serum proteins leak into the alveolus
Continued injury may lead to detachment of the alveolar lining

Question 37

What is bronchopulmonary dysplasia and what can it be caused by?

Answer 37

Abnormal formation of part of the lung

Can be caused by chronic injury to the lungs in preterm infants from mechanical ventilation

Question 38

What is the treatment to prevent respiratory distress syndrome?

Answer 38

1) Glucocorticoid treatment accelerates fetal development and surfactant production
2) Surfactant therapy - natural or artificial

Question 39

What must be present in artificial surfactant for it to be optimally effective?

Answer 39

Surfactant A and B proteins

Question 40

What is surfactant B protein deficiency caused by and what is the prognosis?

Answer 40

Genetic condition - autosomal recessive

Fatal disease even with surfactant replacement therapy