Lecture 4: Respiratory Embryology Flashcards
Where does the respiratory system start from?
Laryngotracheal groove (median outgrowth)
- on the floor of the caudal foregut
- inferior to the 4th pharyngeal arch
What does the endoderm of the laryngotracheal groove give rise to?
Pulmonary epithelium and glands of:
- larynx
- trachea
- bronchi
What does the splanchnic mesoderm of the laryngotracheal groove give rise to?
CT, cartilage, and smooth muscles that surround foregut
What will the laryngotracheal groove evaginate into?
Laryngotracheal diverticulum –> respiratory bud
What is the function of the tracheoesophageal fold?
Divides esophagus (dorsal) from trachea (ventral)
How does the laryngeal inlet form?
Mesenchyme from pharyngeal arches 4 and 6 promote arytenoid swellings, converting primordial glottis into a laryngeal inlet
How does the laryngeal inlet form a bigger opening?
Briefly, over-proliferation of epithelium will occlude the inlet. However, recanalization and apoptosis will remove epithelium revealing a larger inlet and laryngeal ventricles.
Where does the epiglottis develop from?
Hypopharyngeal eminence
-produced from mesenchyme from pharyngeal arches 3 and 4
Where does the trachea develop from?
Laryngotracheal tube
What is a tracheoesophageal fistula?
Abnormal connection between trachea and esophagus
What is the most common form of a tracheoesophageal fistula?
Esophageal atresia: upper esophagus and does not connect with the lower esophagus and stomach
What can cause a tracheoesophageal fistula?
Foregut endoderm does not proliferate fast enough
What are some symptoms of a tracheoesophageal fistula?
Cannot swallow Frequently drools saliva Immediate regurgitation Polyhydramnios Excess air in GI tract
How are primary bronchial buds formed?
From respiratory buds
-grow vetrocaudally and bifurcates
Where do primary bronchial buds grow to?
Grows laterally to pericardioperitoneal canals
How is branching pattern of the lung endoderm initiated?
Splanchnic mesoderm via SHH and FGF 10
What composes a bronchopulmonary segment?
Segmental Bronchi and mesenchyme
What are the four stages of lung maturation?
1) Pseudoglandular
2) Canalicular
3) Terminal Sac
4) Alveolar
What happens in the pseudoglandular state of lung maturation?
Major elements of lungs have formed except those involved with gas exchange
What happens in the canalicular state of lung maturation?
Respiratory bronchioles develop and primordial alveolar structures are present
What happens in the terminal state of lung maturation?
Production of alveoli and pneumocytes
Gas exchange can occur
What happens in the alveolar state of lung maturation?
Mature alveoli is formed
How does splanchnic mesoderm play a role in bronchi development?
1) Cartilaginous plates
2) Bronchial smooth muscle and CT
3) Pulmonary CT and capillaries
What are fetal breathing movements?
Erratic breathing can can cause aspiration of amniotic fluid and stimulate lung development
How is amniotic fluid cleared at birth?
1) Pressure from vaginal birth or via suction tubes
2) Pulmonary capillaries, arteries, and veins
3) Lymphatics
What is pulmonary agenesis?
Complete absence of lung or a lobe
What is oligohydramnios?
Insufficient amniotic fluid volume that can retard lung development
What is pulmonary hypoplasia?
Incomplete development of the lungs due to restriction of fetal thorax
What is respiratory distress syndrome?
Surfactant deficiency that can account for death in half o premature infants
What are congenital lung cysts?
Cyst that can disrupt bronchial development and normal air flow
