Respiratory - Embryology

Question 1

lung development - overview

Answer 1

*occur in 5 stages (embryonic, pseudoglandular, canalicular, saccular, alveolar)
*begins with the formation of the lung bud from the distal end of respiratory diverticulum during week 4 of development

Question 2

lung development - mnemonic for stages

Answer 2

“Every Pulmonologist Can See Alveoli”:

E - embryonic
P - pseudoglandulr
C - canalicular
S - saccular
A - alveolar

Question 3

embryonic stage of lung development

Answer 3

*week s 4-7 of development
*lung bud → trachea → bronchial buds → mainstem bronchi → secondary (lobar) bronchi → tertiary (segmental) bronchi
*note - errors at this stage can lead to tracheoesophageal fistula

Question 4

pseudoglandular stage of lung development

Answer 4

*weeks 5-17 of embryonic development
*endodermal tubules → terminal bronchioles
*surrounded by modest capillary network
*note - respiration impossible, incompatible with life

Question 5

canalicular stage of lung development

Answer 5

*weeks 16-25 of development
*terminal bronchioles → respiratory bronchioles → alveolar ducts
*surrounded by prominent capillary network
* note - airways increase in diameter; pneumocytes develop starting at week 20; respiration capable at week 25

Question 6

saccular stage of lung development

Answer 6

*week 24 of development to birth
*alveolar ducts → terminal sacs
*terminal sacs separated by primary septae

Question 7

alveolar stage of lung development

Answer 7

*week 36 of development to 8 years old
*terminal sacs → adult alveoli (due to secondary septation)

Question 8

breathing in utero vs. after birth

Answer 8

*in utero, “breathing” occurs via aspiration and expulsion of amniotic fluid, leading to increased pulmonary vascular resistance through gestation
*at birth, air replaces fluid, leading to decreased pulmonary vascular resistance