Lung Development & Pathology

Question 1

Stages of Lung Development (5)

Answer 1

Embryonic
Pseudoglandular
Canalicular
Saccular
Alveolar

Question 2

Embryonic Phase

Answer 2

26 days - 6 weeks

Foregut endoderm extends into surrounding mesenchyme

3 rounds of branching establishes lung lobes

Question 3

Pseudoglandular Phase

Answer 3

6 - 16 weeks

14 rounds of branching form terminal bronchioles

Question 4

Canalicular Phase

Answer 4

16 - 28 weeks

Terminal bronchioles divide into respiratory bronchioles

Surfactant production begins

Question 5

Saccular Phase

Answer 5

28 - 36 weeks

Respiratory bronchioles subdivide to produce terminal sacs

Question 6

Alveolar Phase

Answer 6

36 weeks - 4 years

Lungs grow & alveoli mature
Capillary network grows within alveolar wall
Gas exchange units fully established

Question 7

Conducting regions of the lung

Answer 7

16 Generations of conducting airways (from trachea to terminal bronchioles)

Anatomic dead space

Question 8

Respiratory regions of the lung

Answer 8

7 generations of respiratory airways (from respiratory bronchioles to alveoli)

Question 9

Airway epithelium - Bronchi & Bronchioles

Answer 9

Pseudostratified, ciliated epithelim; contains:

1. Ciliated cells - sweep mucin toward esophagus
2. Goblet cells - secrete mucin
3. Basal cells - progenitor cells for goblet and ciliated cells
4. Neuroendocrine cells - secrete granulated serotonin

Question 10

Muscularis

Answer 10

ayer of circumferential smooth muscle; found in large bronchi only

Question 11

Submucosa - Bronchi and bronchioles

Answer 11

Contains:

1. Submucosal glands - mucous and serous secretions
2. Mucosal-associated lymphoid tissue (MALT)

Question 12

Layers of the bronchi wall

Answer 12

Mucosa/Epithelium 
Muscularis 
Submucosa 
Cartilagenous Layer 
Adventitia

Question 13

Layers of the bronchiole wall

Answer 13

Mucosa
Submucosa
Smooth muscle

*Bronchioles DO NOT contain cartilage

Question 14

Clara cells

Answer 14

Found in the mucosal layer of terminal bronchioles

Secrete a surface active substance onto the small airway epithelium

Question 15

Type I Pneumocytes

Answer 15

Cover 90% of the surface of the alveolar septa facing the air space

Terminally differentiated; do not divide

Question 16

Type II Pneumocytes

Answer 16

Progenitors of Type I cells

Secrete surfactant

Question 17

Alveolar macrophages

Answer 17

Phagocytose small particles and bacteria within the alveolar space; leave the alveoli via the muco-ciliary elevator or by lymphatics to function as APCs in the lymph nodes