Respiratory Embryo Flashcards
What is the first step into creating the future respiratory system ?
the development of the laryngotracheal groove in the caudal foregut , inferior to the 4th PAs
Where does the tracheobronchial tree develop?
caudal to the 4th pharyngeal pouches
What is the sequence of events in forming the respiratory system?
laryngotracheal groove -> laryngotracheal diverticulum -> laryngotracheal tube
What does laryngotracheal groove endoderm give rise to?
- pulmonary epithelium
- glands of larynx, trachea, and bronchi
What does the laryngotracheal groove splanchnic mesoderm give rise to?
- CT
- cartilage
- SM
What two dermal layers compromise the laryngotracheal tube?
- foregut endoderm
- splanchnic mesoderm
Describe the steps in formation of laryngotracheal tube
1 - laryngotracheal groove develops in caudal foregut, inferior to 4th PA
2 - groove evaginates to form the laryngotracheal diverticulum
3 - diverticulum elongates and is invested w/ splanchnic mesoderm
4 - distal end of diverticulum = respiratory bud (origin of respiratory. tree)
5 - tracheoesophageal folds fuse and form the tracheoesophageal septum all while above is happening
When do the tracheoesophageal fold become the septum?
end week 5
What layer are the tracheoesophageal folds derived from?
endoderm
What to the tracheoesophageal folds divide the cranial foregut into?
ventral = laryngotracheal tube dorsal = prim. oropharynx and esophagus
what does the laryngotracheal tube give rise to?
- prim. larynx, trachea, brochi, lungs
Where the the larynx being to develop?
@ cranial end of LTT
Name the steps in larynx development
1) mesenchyme swelling appear at cranial end of LTT (arytenoids)
2) arytenoids convert primordial glottis into a T shaped laryngeal inlet
3) inlet closes via epithelium proliferation
4) inlet recanalizes
5) inlet creates a laryngeal vestibule and epiglottis appears
When does recanalization of the larynx happen?
by end of week 10
What does the laryngeal vestibule contain?
-> contains mucous membrane folds which create vocal and vestibular folds
How is the epiglottis formed?
Via the hypo pharyngeal eminence
Where are laryngeal m. derived from ?
myoblasts of 4th and 6th PA
Where is the epiglottis derived from?
mesenchyme of 3rd and 4th PA
What are the 3 layers that make up the larynx?
- epidermis
- cartilage
- muscles
Where is laryngeal epidermis derived from ?
foregut endoderm (from LTT)
Where is cartilage of larynx derived from?
NCC of 4th and 6th PA
What does the laryngotracheal diverticulum give rise to?
trachea and primary bronchial buds
What dermal layer gives rise to tracheal epithelium and glands?
foregut endoderm
What dermal layer gives rise to the tracheal cartilage, CT, & SM?
splanchnic mesenchyme
Describe the steps of lung development from the LTT
1) distal end of laryngotracheal diverticulum enlarges to form the respiratory bud (wk 4)
2) bud grown ventrocaudally and bifurcates
3) during 5th week 1ry bronchi -> 2ndry bronchi -> 3ry bronchi
4) bronchopulmonary segments appear by wk 7
What regulates the branching pattern of the developing lungs?
splanchnic mesenchyme
When do you start to see 1,2,3ry bronchi
5th week
When do bronchopulmonary segments form?
7th week
What is a tracheoespohageal fistula?
abnormal connx b/w trachea and esophagus
(lower respiratory tract)
-assoc. w/ esophageal atreasia
What causes a tracheoesophageal fistula?
result of failure of foregut endoderm to proliferate rapidly enough in relation to developing embryo
Presenting symptoms of a tracheoesophageal fistula?
- cannot swallow
- drool
- immediate regurgitation
- polyhydramnios (amniotic fluid cannot enter stomach to be recycled via placenta)
what are the stages of lung maturation?
pseudo glandular -> canalicular -> terminal sac -> alveolar
What characterizes the pseudo glandular stage?
5-17 weeks
- looks like exocrine gland
- all major structures except gas exchange ones
- NOT SURVIVABLE
What characterizes the canalicular stage?
16-25 weeks -vascularization -respiratory bronchioles -1ry alveolar and sacs present (primitive alveoli) MAY OR MAY NOT SURVIVE
What characterizes the terminal sac stage?
24 weeks -birth -numerous alveoli -thin epic, high vascularization -Type 1 & 2 pnumeocytes ; lymph capillaries GAS EXCHANGE CAN OCCUR
SURVIVABLE
What is a major determinant of fetal survivability in lung maturation stage?
-development of capillaries
more capillary development = high survivability
What characterizes the alveolar stage?
32 weeks - 8 years
- alveolocapillary membrane
- primitive alveoli form more primitive alveoli
- mature alveoli
Alveolar development is largely completed by what year of life?
3
What does splanchnic mesoderm create in the developing bronchial/resp bud?
1) cartilaginous plates (bronchial)
2) bronchial SM & CT
3) pulmonary CT and capillaries
What are fetal breathing movements?
intermittent patterns that conditions respiratory m -> essential for lung development
causes: inspiration of amniotic fluid
* early predictor if fetal outcome in preterm delivery
What is laryngeal atresia?
RARE
-obstruction of upper fetal airway (CHAOS)
What causes laryngeal atresia?
failure of recanalization of laryngeal inlet
What are symptoms of laryngeal atresia?
lungs enlarged ; dilated airways -> filled with fluid
diaphragm flattened or inverted ; fetal ascites or hydros
What is pulmonary agenesis?
complete absence of a lung to lobe and accompanying bronchi
What causes pulmonary agenesis?
respiratory bud fails to split into R/L bronchial buds
What is Oligohydramnios?
insufficient amniotic fluid production (<500 ml)
severe = retards lung development
what is oligohydramnios assoc. with?
renal agenesis/failure in fetus
Pulmonary hypoplasia is a result of?
restriction on fetal thorax due to uterine pressure
- dec. hydronic pressure on lungs
- affects stretch receptors and lung growth
exacerbated by oligohydroamnios < 26 wks
What is oligohydramnios (potter’s) sequence?
atypical physical appearance if baby due to oligohydramnios when in utero
- clubbed feet ; pulmonary hypoplasia ; cranial anomalies ; limb hypoplasia
What is respiratory distress syndrome?
rapid, labored breathing developed shortly after birth
major cause: surfactant deficiency
-50-70% of premie deaths
What are the mechanisms behind respiratory distress syndrome?
lungs under inflated ; alveoli filled with fluid that resembles glassy membrane
-irrev. changes in type 2 cells making them incapable of producing surfactant
What are symptoms of RDS?
- tachypnea, nasal flaring
- suprasternal, intercostal, subcostal retractions
- grunting
- cyanosis
What are congenital lung cysts?
cause : formed by dilation of terminal bronchioles
- filled with fluid/air
- disturbance of bronchial deep. during late fetal life
Symptoms of congenital lung cysts?
wheezing
cyanosis
difficulty breathing
What is developed by week 4 ?
respiratory diverticulum -> resp. bud
What is developed by week 5?
tracheoespohageal folds -> septum
1ry bronchi -> 2ndry ->3ry
When are terminal bronchioles developed?
week 16
What is developed by week 28?
respiratory bronchioles, 1st terminal sacs
What is developed by week 36?
terminal sacs -> mature alveoli
