RESP-embryology Flashcards
where is the respiratory system derived from?
foregut
what does the respiratory system begin as?
as an outgrowth from endodermic foregut, just inferior to the pharynx = tube of endoderm
what is the laryngotracheal opening?
The opening that still connects diverticulum to pharynx
what is the respiratory bud?
elongated laryngotracheal diverticulum
what does the endodermal lining of the laryngotracheal groove give rise to in the 4th week of development?
trachea, bronchi and tracheobronchial tree, glands of larynx
what does the splanchnic mesoderm of the laryngotracheal groove give rise to in the 4th week of development?
connective tissue, cartilage and smooth muscle of these structures
what happens to the laryngeal groove at the end of the 4th week of develop?
evaginates to form laryngotracheal diverticulum -Elongates distally to form a globular ‘respiratory bud’
what does the respiratory bud divide into?
2 outpouchings
-primary bronchial buds
what happens to the bronchial buds divide into bronchioles?
they grow into pleura formed by mesoderm
what are the 2 types of pleura?
visceral pleura
parietal pleura
where is the visceral pleura derived from?
splanchnic mesenchyme
where is the parietal pleura derived from?
somatic mesoderm
what are the 4 stages of lung maturation?
- pseudoglandular
- canalicular
- terminal sac
- alveolar
which weeks of development is the pseudoglandular stage?
6-16 weeks
which weeks of development is the canalicular stage?
16-26 weeks
which weeks of development is the terminal sac stage?
26 weeks to birth
which weeks of development is the alveolar stage?
32 weeks to 8 years old
describe the events of the pseudoglandular stage?
-Epithelial tubes lined with cuboidal epithelial
cells
-all major elements have formed, except those involved in gas exchange
-Respiration is NOT POSSIBLE, foetuses
born at this stage unable to survive
what do the developing lungs resemble in the pseudoglandular stage?
exocrine glands
describe the events of the canalicular stage?
• Lumen of bronchi + terminal bronchioles
become larger
• tissue becomes highly vascularised
• By 24 weeks = terminal bronchiole gives
rise to 2 or more respiratory bronchioles but cannot be used due to lack of surfactant
(Divide to form primordial alveolar ducts)
• Respiration IS POSSIBLE because of
primordial alveolar sacs and vascularisation
describe the events of the terminal sac stage?
• More terminal sacs develop
• Epithelia becomes a lot thinner to become more closely related to alveolar capillaries
• Adequate gas exchange can now take place
if fetus is born at 26+ weeks
• Type II pneumocytes form
what do type 2 pneumocytes secrete?
surfactant
describe the events of the alveolar stage?
• Sacs comparable to alveoli are present at 32
weeks
• Epithelial lining becomes a thin, squamous
epithelial layer – type I pneumocytes
• Adjacent capillaries bulge into alveolar
saccules
• By late fetal stage, lungs are capable of
respiration because alveolar capillary
membrane is sufficiently thin to allow gas
exchange
what is the size increase of the lungs postnatally due to?
due to the number of respiratory bronchioles and alveoli increasing, NOT because the existing amount increase in size
