Respiratory Embryology Flashcards
What does the laryngotracheal groove become?
When does it develop?
pulmonary epithelium
glands of larynx, trachea & bronchi
week 4
What does the splanchnic mesoderm (from lat plate) of laryngotracheal groove become?
CT, cartilage & smooth muscle of respiratory system (surrounds the foregut)
Where does the lung bud come from?
laryngotracheal diverticulum (evagination of laryngotracheal groove)
Why are the tracheoesophageal folds important? When do they fuse?
endodermal ingrowth of laryngotracheal tube that fuses to form tracheoesophageal septum (by end of week 5)
divides cranial portion of foregut & separates respiratory system from digestive system
fuse during week 5
Where is the laryngotracheal tube located by end of week 5?
ventral part of foregut
primordium larynx, trachea, bronchi & lungs
What does the dorsal part of the tracheoesophageal septum become?
primordium oropharynx & esophagus
Where does the epithelial lining of the larynx come from?
endoderm of laryngotracheal tube
Where do the cartilages & CT of larynx come from?
mesenchyme of PA 4 & 6
What is the result of the proliferation of the laryngotracheal tube endoderm?
occlusion of the lumen of the tube
When does recanalization occur and what is the result?
during week 10
true vocal folds & vestibular folds in the larynx
Where does the epiglottis come from?
hypopharyngeal eminence (mesenchme of PA 3 & 4)
Where do the laryngeal muscles come from?
myoblasts of PA 4 & 6
What does the division of the laryngotracheal diverticulum produce?
trachea (late week 4/early week 5)
Endoderm derivatives of trachea
tracheal epithelium
tracheal glands
pulmonary epithelium (lining of lungs)
Splanchnic mesenchyme derivatives of trachea
tracheal cart (hyaline cart)
tracheal CT
tracheal smooth m
Why is splanchnic mesenchyme important in respiratory development?
lung development requires SM to signal for bronchial bud branching in week 5
Visceral pleura
splanchnic mesoderm of lateral plate
Parietal pleura
somatic mesoderm of lateral plate
4 stages of prenatal lung development
Pseudoglandular (weeks 5-17)
Canalicular (weeks 16-25)
Terminal sac (week 24-birth)
Alveolar (week 32-8yo)
Pseudoglandular stage
weeks 5-17
all major elements of lung formed
no alevoli for gas exchange
fetus is NOT survivable
Canalicular stage
weeks 16-25
vascularization
resp bronchioles + primordial alevolar & sacs
fetus is +/- survivable
Terminal sac stage
week 24-birth
increase # of alveoli
vascularization of thin epithelium
Type 1 & Type 2 pneumocytes
lymph capillaries
survivable b/c gas xchange can occur!
Alveolar stage
week 32-8yo
alveolocapillary membrane
primitive & mature alveoli (95% of alveoli mature post-natally)
What stage of lung development is the fetus definitely survivable?
terminal sac stage (week 24-birth) b/c has necessary components for proper gas exchange
How is splanchnic mesoderm critical for bronchi development?
as alveoli are added, need to keep developing other supporting tissue & needed for:
bronchial cartilage plates
bronchial smooth m & CT
pulmonary CT & capillaries
Largyngeal atresia
failure of laryngeal recanalization in week 10
obstructed upper fetal airway
airways dilated, lungs large & filled w/ fluid, diaphragm may be flat or inverted
Tracheoesophageal atresia
abnormal connection btwn trachea & esophagus due to failure of foregut endoderm to proliferate in relation to whole embryo
can’t swallow, drool, regurgitate food (GI contents can reflux thru fistula into trachea & lungs)
lung development can be impaired
Pulmonary agensis
failure of splitting of R & L bronchial buds from respiratory bud
complete absence of lung or lobe & its accompanying bronchi
Oligohydramnios
pulmonary hypoplasia due to insufficient amniotic fluid production (renal issue)
restricted fetal thorax from uterine pressure
clubbed feet, compressed face, issues w/ hand placement & breech position
Respiratory Distress Syndrome
due to surfactant deficiency (type 2 pneumocytes can’t produce surfactant)
lungs are underinflated & alveoli appear glassy
grunting, cyanosis
Role of surfactant
produced by type 2 pneumocytes
keeps surface tension @ min (btwn air/liquid interface) w/ in alveoli of lungs & prevents lung collapse during expiration
Congenital lung cysts
issue w/ bronchial development due to abnormal dilation of terminal bronchi in late fetus
cysts are filled w/ fluid or air
wheezing, cyanosis, issues breathing
Fetal Breathing Movements
critical for proper lung develop (conditioning of respiratory muscles)
forceful aspiration of amniotic fluid stimulates lung development
amniotic fluid is replaced by air in alveoli @ birth
How is amniotic fluid in lungs cleared?
released from mouth/nose via pressure on fetal thorax during vaginal delivery
absorbed by pulmonary capillaries, arteries & veins
absorbed by lymphatics
