Embryology

Question 1

What is the first stage of lung maturation and when does it take place?

Answer 1

Embryonic stage
26 days-6 weeks
Respiratory diverticulum forms initial branching to give lungs, lobes and segments

Question 2

What is the second stage of lung maturation and when does it take place?

Answer 2

Pseudoglandular stage
6-16 weeks
14 more generations of branching: terminal bronchioles

Question 3

What is the third stage of lung maturation and when does it take place?

Answer 3

Canalicular stage
16-28weeks
Terminal bronchioles to 2 or more respiratory bronchioles to 3-6 alveolar ducts

Question 4

What is the fourth stage of lung maturation and when does it take place?

Answer 4

Saccular stage
28-36 weeks
Terminal sacs form; capillaries establish close contact

Question 5

What is the fifth stage of lung maturation and when does it take place?

Answer 5

Alveolar stage
36 weeks - early childhood
Alveoli mature

Question 6

Which germ layers is the respiratory system derived form?

Answer 6

The respiratory system begins to develop as an endodermal outgrowth from the pharyngeal gut and later receives contributions from cells of the splanchnic mesoderm.

Question 7

Describe Type I alveolar cells

Answer 7

They make up 97% of the alveolar surfaces

Thin squamous cells specially designed to serve as gas-permeable components of the blood-air barrier

Question 8

Describe Type II alveolar cells

Answer 8

They make up 3% of the alveolar surfaces
Interspersed between the Type I cells
Cubiodal cells that produce surfactant

Question 9

What is the importance of type II cells in reducing respiratory distress syndrome

Answer 9

RDS is due to surfactant deficiency and immature lung development - Type II cells produce surfactant