Development of respiratory system; Larynx, Trachea, Lungs and esophagus

Respiratory system

Origin: Endodermal floor of pharynx behind hypobanchial eminence

1. Epithelium

  • Laryngo-tracheal groove appears in the endodermal floor of pharynx behind hypobranchial eminence
  • Edges of groove unite dividing upper foregut into esophagus and laryngo-tracheal tube
  • Laryngo- tracheal tube grows caudally:
  1. Upper end – larynx
  2. Then – trachea
  3. Lower part – 2 lung buds
  • Right lung bud divides into 3 branches (main bronchii)
  • Left  lung bud divides into 2 bronchii
  • Each bronchus – subdivisions – bronchial tree
  • Terminal/respiratory bronchioles end in alveoli, expand only after birth

 

2. Cartilage, muscles and connective tissue: 4th and 6th arch mesoderm

  • 4th pharyngeal arch  – thyroid cartilage, cricothyroid muscle
  • 6th pharyngeal arch – cricothyroid, arytenoid, cuneiform and corniculate cartilages, and all other laryngeal muscles

NB: Splanchnic and somatic pleura forms lungs viceral and parietal pleura

Image result for laryngotracheal groove

 

Maturation of lungs:

Image result for maturation of lungs

 

Image result for maturation of lungs

 

Image result for maturation of lungs

 

Anomalies of lungs:

  • Agenesis of one or both
  • Acessory lung lobe
  • Hyaline membrane disease – alveoli cannot ventilate adequetly due to absence of surfactant

 

Esophagus

Origin: Endoderm of foregut

  • From respiratory diverticulum to stomach swelling
  • Surrounding mesenchyme forms musculature of esophagus

 

Anomalies of trachea and esophagus:

  1. Tracheal-esophageal fistula – incomplete fusion of laryngo-tracheal groove
  2. Esophageal atresia – narrowing of esophagus
  3. Failure of elongation – pulls stomach up thorax – Hiatus hernia
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