9 Development of Respiratory System

Question 1

Origin of respiratory diverticulum/lung bud.

Answer 1

Laryngotracheal groove in floor of caudal pharynx.

Endodermal outgrowth ventrally –> lung bud/respiratory diverticulum.

Question 2

Structure to separate trachea from esophagus.

Answer 2

Tracheoesophageal septum separates lung bud (ventrally) from foregut (dorsally).

Question 3

Connection between pharynx and respiratory diverticulum.

Answer 3

Primordial laryngeal inlet.

Question 4

Two common defects in TE septum –> result?

Answer 4

1. Tracheoesophageal fistula (abnormal connection, just superior to main bronchi split).
2. Esophageal atresia (blocked, due to posteriorly deviating septum).
   Result: polyhydramnios (too much amniotic fluid)

Question 5

Lung bud derivatives

Answer 5

larynx, trachea, respiratory tree, lungs

esophagus from foregut

Question 6

Epithelial lining + glands of airways?

Answer 6

Endoderm

Question 7

Smooth muscle + CT of airways?

Answer 7

Splanchnic mesoderm

Question 8

Laryngeal cartilages and musculature from…?

Exception?

Answer 8

Pharyngeal arch pairs 4 & 6.

Epiglottis is exception! From mesenchyme of caudal hypopharyngeal eminence.

Question 9

Innervation of 4th arch?

Answer 9

Superior laryngeal n.

Question 10

Innervation of 6th arch?

Answer 10

Recurrent laryngeal n.

Question 11

Respiratory Tree Branching

Answer 11

Know it! :)

Question 12

Lung bud divides…

Answer 12

2 primary bronchial buds

Extend into pericardioperitoneal canals (future pleural cavities)

Question 13

Primary bronchial buds divide…

Answer 13

secondary (lobar) bronchial buds

3 on R, 2 on L

Question 14

Secondary/lobar bronchial buds divide…

Answer 14

tertiary (segmental) bronchial buds

10 on R, 8-9 on L

Question 15

Visceral pleura of lungs from…?

Answer 15

splanchnic mesoderm

Question 16

Parietal pleura from…?

Answer 16

somatic mesoderm

Question 17

Cause of respiratory distress syndrome?

Answer 17

Premature baby, insufficient surfactant.

24-26 weeks.

Question 18

Function of pulmonary surfactant?

Answer 18

Lines inner wall of alveolus.
Reduces surface tention at air-alveolar interface.
Prevents alveolar collapse upon exhaling.

Question 19

Cells that produce pulmonary surfactant?

Answer 19

Type II cells, at week 20-22.

Insufficient before 26-28.

Question 20

1st stage of lung development

Answer 20

Pseudoglandular (6-16)
Exocrine glands.
All but most distal portions of respiratory tree (respiratory bronchioles, alveolar sacs).
Will NOT survive.

Question 21

2nd stage of lung development

Answer 21

Canalicular (16-26)
Highly vascular lung tissue.
Terminal bronchiole –> 2+ respiratory bronchioles, with primitive alveolar ducts.
Some to terminal sacs (primitive alveoli).
MAY survive (if late).

Question 22

3rd stage of lung development

Answer 22

Terminal Sac (26-birth)
More terminal sacs (primitive alveoli) hugged by capillaries --> blood/brain barrier.
At 26 weeks: Type I alveolar cells = simple squamous, gases diffuse.
Type II alveolar cells = pulmonary surfactant.

Question 23

4th stage of lung development

Answer 23

Alveolar (32 wks - 8 yo)
Alveoli fully functional.
95% of mature alveoli develop postnatally.
Continue to develop up to 8 years.

Question 24

What embryonic germ layer gives rise to the smooth muscle in the walls of the bronchioles?

Answer 24

splanchnic mesoderm

Question 25

Which of the following is most consistent with the pseudoglandular stage of lung development?
A.) Weeks 6-16, no respiratory bronchioles, no terminal sacs
B.) Weeks 6-16, respiratory bronchioles, no terminal sacs
C.) Weeks 16-26, blood-air barrier is established
D.)Weeks 16-26, tissue is highly vascular, no blood-air barrier
E.) Weeks 32 – birth, terminal sacs present with types I + II alveolar cells

Answer 25

A.) Weeks 6-16, no respiratory bronchioles, no terminal sacs