ANA 206 Development of the Lungs

Question 1

Stages of lung development

Answer 1

1. Pseudoglandular
2. Canalicular stage
3. Terminal sac (saccular) stage
4. Alveolar stage

Question 2

Pseudoglandular stage

Answer 2

5-16 weeks
* Bronchial tree is formed up to terminal bronchioles
* Elements of the bronchial tree involved in respiration (e.g., respiratory
bronchioles, alveolar ducts, and alveoli) are not formed
* Respiration is not possible at this stage; hence premature fetuses cannot
survive if born at this stage

Question 3

Canalicular stage

Answer 3

16–26 weeks
* Respiratory bronchioles and alveolar ducts are formed
* Few alveolar sacs are also formed
* Lung tissue is well vascularized
* Fetus born at the end of the stage can survive if given intensive care

Question 4

Terminal sac (saccular) stage

Answer 4

26 weeks to birth
* Large number of terminal sacs (primitive alveoli) develop
* Capillaries bulge into developing sacs
* Intimate contact develops between epithelium of sac and endothelium of
capillary to permit adequate exchange of gases for survival of fetus, if born
prematurely. Fetuses born at this stage survive

Question 5

Alveolar stage

Answer 5

8 months to 8 years
* Formation of definitive (true) alveoli with an increase in their number
* Type II pneumocytes produce a sufficient amount of surfactant
* Free exchange of gases across the blood–air barriers formed by epithelium of
alveoli and endothelium of capillaries