respiratory embryo. - Cole Flashcards
respiratory diverticulum (lung bud) appears as an outgrowth from the ventral wall of the foregut in week..
4
appearance, locaiton of lung dependent upon
increase in retinoid acid (RA) produced by adjacent mesoderm
- which upregulates TBX4 expressed in endoderm of gu tube at site of resp. diverticulum.
- TBX4 induces formation of th e ‘bud’ and continued growth and differentiation of the lungs
endoderm gives rise to
- epithlium of internal lining of the larynx
- trachea
- bronchia
splanchnic mesoderm gives rise to
-cartilaginous, muscular, CT components of trachea and lungs
describe differentiaiton of lung buds from foregut
- initially open communication
- diverticulum expands caudally, 2 longidutinal ridges the ‘tracheoesophageal ridges’ separate from the foregut
- then fuse to form ‘tracheoesophageal septum’ which divides dorsal portion into esophagus and ventral portion, the trache and lung buds
resp. primordium maintains its communicaiton with the pharynx through the
laryngeal orifice
improper separation of esophagus and trachea by the tracheoesophageal septum can result in
- esophageal atresia with or w/o tracheoesophageal fistulas (TEFs)
- 90% result in upper portion of esophagus ending in a blind pouch and lower segment forming fistula
4% are isolated esophageal atresia nad H-type TEFs
TEFs are a component of…, a collection of defects of unknown causation, occuring more frequently than predicted by chance alone
VACTERL association
- Vertebral anomalies
- Anal atresia
- Cardiac defects
- TEF
- Esophageal atresia
- Renal anomalies
- limb defects
indicative of TEF, can be picked up on ultrasound
- polyhydramnios
- amnioitic fluid doesn’t pass ot stomach and instestine
- gastric contents/ amnoitic fluid at birth may enter trachea through a fistula, causing pneumonitis and pneumonia
during its separation from the foregut, the lung bud forms the…
trachea
- two lateral outpocketings, the bronchial buds (week 5)
week 6: primary bronchi
week 8: secondary bronchi
the narrow spaces for the lungs lying on each side of the foregut
pericardioperitoneal canals
mesoderm, covering the outside of the lung, forms the
visceral pleura
somatic mesoderm, covering the body wall from the inside becomes the
parietal pleura
space b/w the parietal and visceral pleura is the
pleural cavity
secondary bronchi to tertiary
2ndary divide repeatedly in a dichotomous fashion, forming 10 tertiary (segmental) bronchi in right lung, and 8 in left, creating the ‘bronchopulmonary segments’ of adult lung
before the bronchial tree reaches its final shape..
an additional six divisions form during postnatal life
signals for branching emit form the mesoderm and involve
FGFs
sufficient no. of mature alveolar sacs and capillaries are present to guarantee adequate gas exchange and ensure premees survivability by the end of the
seventh month
terminal bronchioles divide to form.. which divide..
form resp. bronchioles which further divide into 3-6 alveolar ducts
- ducts end in ‘terminal sacs’ (primitive alveoli) surrounded by flat alveolar cells in close contact w/ neighboring capillaries
importance for fetal breathing movements?
- begin before birth, cause aspiration of aminiotic fluid
- important for stimulating lung development and conditioning resp. muscles
without surfactant…
alveoli would collapse during expiration (atelectasis)
surfactant offsets this surface tension
explain role of surfactant and macrophages in delivery
- during 34th week, some of the surfactant enters amniotic fluid and acts on macrophages in the amniotic cavity
- macrophages get activates, migrate across chorion into uterus and begin producing Interleukin-1 beta
- upregulation of these upregulates prostaglandins which cause uterine contractions
absent or insufficient surfactant in premature baby causes
respiratory distress syndrome (RDS)
- because of collapse of the primitive alveoli (hyaline membrane disease)
growth of the lungs after birth is primarily due to
an increase in the no. of resp. bronchioles and alveoli
- and NOT due to an increase in alveolar size.
- new alveoli formed during first 10 years of postnatal life
