Embryology

Question 1

Where is the respiratory diverticulum/lung bud found?

Answer 1

The ventral wall of the foregut

Question 2

Which germ layer is the foregut a part of?

Answer 2

Endoderm

Question 3

On what day do the lung buds appear?

Answer 3

22

Question 4

What separates the respiratory diverticulum from the foregut?

Answer 4

Tracheoesophageal ridges

Question 5

What is a tracheoesophageal fistula (TOF)?

Answer 5

Incomplete division of foregut into oesophageal and respiratory portions.

Question 6

What is the most common (85-90%) TOF?

Answer 6

oesophageal atresia

Question 7

What is the second most common TOF?

Answer 7

connection of oesophagus to trachea

Question 8

What are the symptoms of tracheoesophageal fistula with oesophageal atresia?

Answer 8

Abdomen rapidly distends as fills with air
Regurgitation of milk
Coughing
Stomach acid and bile in trachea- infection

Question 9

What are the symptoms of a connection between the oesophagus and trachea?

Answer 9

Milk in respiratory system

No regurgitation as can still swallow milk

Question 10

Which other congenital abnormalities are TOFs usually associated with?

Answer 10

VACTERL:

Vertebral defects (spina bifida)
Anal atresia
Cardiac defects -1/3 OF CASES
Tracheoesophageal fistulas 
Oesophageal atresia
Renal abnormailities
Limb defects  (common)

Question 11

During what week are the lobar bronchi formed?

Answer 11

5

Question 12

During what week are tertiary bronchi formed?

Answer 12

6

Question 13

How many lobar bronchi are in each lung?

Answer 13

3 on right, 2 on left

Question 14

How many tertiary bronchi are in each lung?

Answer 14

10 on right, 8 on left

Question 15

When are terminal bronchioles formed?

Answer 15

Week 16

Question 16

When are respiratory bronchioles formed?

Answer 16

Week 26

Question 17

When do the first alveoli develop?

Answer 17

Week 36

Question 18

How is branching partially regulated?

Answer 18

Interaction of the epithelium (from foregut) with the overlying visceral mesoderm (which will form cartilage, smooth muscle, connective tissue and capillaries)

Question 19

From where are the capillaries, smooth muscle, cartilage and connective tissue derived?

Answer 19

The visceral mesoderm.

Question 20

What are the visceral and parietal pleura derived from?

Answer 20

Visceral and parietal mesoderm.

Question 21

What is pulmonary agenesis?

Answer 21

When the lung bud fails to split resulting in the complete absence of bronchi and vasculature. Unilateral or bilateral. Bilateral is incompatible with life.

Question 22

What is pulmonary hypoplasia?

Answer 22

All components present but incompletely developed. Severity varies. May be in association with congenital diaphragmatic hernia.

Question 23

What is branching morphogenesis?

Answer 23

Extra lobes or segments- little functional significance.

Question 24

What are the four periods of lung maturation?

Answer 24

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

Question 25

When is the pseudoglandular period?

Answer 25

5-17 weeks

Question 26

What happens during the pseudoglandular period?

Answer 26

The respiratory tree branches to form terminal bronchioles. Respiration not possible

Question 27

When is the canalicular period?

Answer 27

16-25 weeks

Question 28

What happens during the canalicular period?

Answer 28

Terminal bronchioles give rise to respiratory bronchioles which give rise to alveolar ducts. Mesodermal tissue becomes highly vascularised. Respiration possible towards the end.

Question 29

When is the terminal sac period?

Answer 29

26 weeks - birth

Question 30

What happens during the terminal sac period?

Answer 30

Further terminal sacs develop Epithelium thins and capillaries come into 'contact' with it Blood-air barrier formed Type I and type II pneumocytes formed from differentiation of epithelium Surfactant produced, facilitating inflation. Survival possible but may have respiratory distress syndrome

Question 31

When is the alveolar period?

Answer 31

36 weeks-8 years

Question 32

What happens during the alveolar period?

Answer 32

Increase in number of respiratory bronchioles and alveoli (95% mature alveoli don't develop until after birth)

Question 33

When do breathing movements start?

Answer 33

In utero, to remove amniotic fluid and to practice muscles of respiration

Question 34

What happens to lung fluid after birth?

Answer 34

It is reabsorbed into the capillaries

Question 35

How is infant respiratory distress syndrome treated?

Answer 35

- Glucocorticoid treatment accelerates foetal lung development and surfactant production - Surfactant therapy- natural or artificial

Question 36

What genetic condition can also affect surfactant?

Answer 36

Surfactant protein B deficiency disease Fatal even with replacement therapy. This protein only makes up 2% of surfactant but is very important. Autosomal recessive.