Lecture 4: Respiratory Embryology Flashcards
When does the respiratory system start to develo
Describe the initial development of the respiratory system?:
Wk 4
Caudal to PA 4 > laryngotracheal groove grows forward from developing foregut > laryngotracheal diverticulum (lung bud) separates from foregut tube > mix with mesenchyme > respiratory bud > tracheobronchial tree
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? When does this happen?
Endoderm > the folds fuse > tracheoesophageal septum that divides esophagus (dorsal) from trachea (ventral)
Week 5
How do the laryngeal cartilages form?
How does the larynx epithelium form?
4th and 6th PA mesenchyme > cartilage (mostly NCC derived) > form laryngela inlet
cranial endoderm of laryngotracheal tube > epithelium > proliferates as the growth inlet forms and airway is cleared at recanalization
How does the laryngeal inlet form and how does it make a bigger opening?
Cartilage grows into the T shaped laryngeal inlet > epithelium proliferates and blocks the lumen
Via recanalization at wk 10 > apoptosis of epithelium cells reopens the lumen > formation of laryngeal ventricles which lead to vocal and vestibular folds
How does the epiglottis form?
PA 3 and 4 mesenchyme > hypo-pharyngeal eminence > epiglottis
How does the trachea form?
How does the tracheal connective tissue, cartilage and muscle form?
Laryngotracheal diverticulum > endoderm > trachea, pulmonary epithelium and glands
Laryngeotracheal diverticulum > splanchnic mesenchyme > tracheal CT, cartilage and muscle
What is a tracheoesophageal fistula? What causes it?
Abnormal connection between trachea and esophagus due to foregut endoderm failing to proliferate rapidly
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 are some symptoms of a tracheoesophageal fistula?
Cannot swallow Frequently drools saliva Immediate regurgitation Polyhydramnios (excess amniotic fluid) Excess air in GI tract
Timeline of lung formation
Laryngeotracheal diverticulum > Respiratory bud > distal end bifurcation to form the primary bronchial buds (“tree”) at Wk 4 > Wk 5: secondary and tertiary bronchial buds form > Wk 7: bronchopulmonary segments (bronchi + mesenchyme)
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?
When is this happening?
Major elements of lungs have formed except those involved with gas exchange
Week 5-17
What happens in the canalicular state of lung maturation?
When is this happening?
Respiratory bronchioles develop and primordial alveolar structures are present, baby may or may not survive (need surfactant to survive)
Week 16 - 25
What happens in the terminal state of lung maturation?
When is this happening?
Production of alveoli and pneumocytes (Type II - surfactant)
Gas exchange can occur, so survivable
Wk 24 - birth
What happens in the alveolar state of lung maturation?
When is this happening?
Mature alveoli is formed from primitive alveoli
Wk 32 - 8 yo
What structures form from the splanchnic mesoderm?
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, causing baby to swallow amniotic fluid to 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? What causes this?
Complete absence of lung or a lobe due to failure of bud to split in 2
What is oligohydramnios? What organ disease is this usually related to?
Insufficient amniotic fluid volume that can retard lung development
Kidney failure
What causes pulmonary hypoplasia? What are the symptoms?
restricted fetal thorax > low pressure > decrease hydraulic pressure in lungs > Incomplete development of the lungs and oligohydramnios (insufficient)
What is respiratory distress syndrome?
Symptoms?
Surfactant deficiency that can account for death in half of premature infants
Decreased lung inflation and alveolar membrane is hyaline like and has abnormal Type II pneumocytes
What are congenital lung cysts?
Cyst formed from terminal bronchi dilations that can disrupt bronchial development and normal air flow
Why do babies have higher risk of choking?
Neonates have higher larynx that descends within the 1st 2 years
What is laryngeal atresia and what condition is this related to?
What are the symptoms of this condition and how is it treated?
recanalization does not occur > obstructed upper airway
CHAOS syndrome: dilated airways, enlarged and fluid filled lungs, inverted or flat diaphragm.
Treated with endoscopic dilation
From what does pleura form? What parts form visceral and parietal pleura?
Lateral plate mesenchyme > splanchnic > visceral pleura
Lateral plate mesenchyme > somatic > parietal pleura
