Respiratory system

• Respiratory system

  A series of air passages and a pair of lungs with air spaces (alveoli)

  
• Functions of the respiratory system

  • Air conduction
  • Air filtration
  • Speech
  • Sense of smell
  • Endocrine
  • Gaseous exchange

  
• Divisions of the respiratory system


  • Conducting passages
  • Respiratory units of the lung

  
• Conducting passages of the respiratory system


  • Nasal cavities, air sinuses
  • Trachea
  • Intrapulmonary bronchus
  • Bronchioles
  • Terminal bronchiole

  
• Respiratory units of the lung


  • Respiratory bronchiole
  • Alveolar duct
  • Alveolar sac
  • Alveoli (including interalveolar septum & blood-air barrier)

  
• General pattern of the respiratory tract

  • Mucosa (epithelium, lamina propria, muscularis mucosa)
  • Submucosa
  • Cartilage
  • Adventitia/Serosa

  
• Nasal cavity


  • Olfactory mucosa
  • Respiratory mucosa

  
• Nasal cavity patterns -Olfactory mucosa


  • Olfactory epithelium + basement membrane
  • Vascular lamina propria with olfactory or Bowman's glands
• Nasal Cavity pattern - Respiratory mucosa


  • Respiratory epithelium (5 cell types)
  • Vascular lamina propria with mucous glands and elastic fibres

  
• Epithelium in nasal cavity


  • Respiratory mucosa: Ciliated columnar, goblet, brush, small granule, basal cells
  • Olfactory mucosa: Sustentacular, brush, olfactory, basal cells

  
• Trachea pattern


  • Mucosa (respiratory epithelium, lamina propria)
  • Submucosa (dense irregular CT, C-shaped hyaline cartilage, mucous-serous glands, trachealis muscle)
  • Adventitia (CT binding to adjacent structures)
  • No muscularis mucosa in trachea

  
• Location of trachealis muscle

  Function is to facilitate air flow
• Intrapulmonary bronchus


  • Mucosa (respiratory mucosa, smaller lamina propria, muscularis mucosa)
  • Submucosa (loose CT, glands, adipose, discontinuous cartilage plates)
  • Adventitia (dense CT continuous with adjacent structures)

  
• Bronchiole pattern


  • Mucosa (epithelium transitions, thin lamina propria, thick circular muscularis mucosa)
  • Submucosa (relatively thick CT, no glands or cartilage)
  • Adventitia (thin loose CT)
• Terminal bronchiole pattern


  • Mucosa (ciliated simple cuboidal epithelium with Clara cells, thick circular muscularis mucosa and elastic fibres)
  • Submucosa (relatively dense CT, no glands or cartilage)
  • Adventitia (thin loose CT)
• Respiratory bronchiole pattern


  • Mucosa (proximally ciliated cuboidal, distally Clara cells predominate, supported by SM and elastic fibres, alveoli scattered along length)
  • Branches into alveolar duct

  
• Inter-alveolar septum pattern


  • Thin lamina propria with CT fibres and capillaries
  • Contains type I pneumocytes, type II pneumocytes, macrophages
  • Site of blood-air barrier

  
• Alveolus


  • Sac-like pocket lined by simple squamous epithelium
  • Thin CT between alveoli
  • Associated with capillaries to facilitate gaseous exchange
  • Contains type I pneumocytes and type II pneumocytes

  
• Blood-air barrier


  • Thin layer of surfactant
  • Pneumocyte type I cell
  • Fused basal lamina
  • Endothelial cells
• Asthma is characterised by reversible bronchoconstriction, luminal obstruction by mucous, and vasodilation of bronchial microvasculature
• COPD is characterised by inflammatory response, alveolar wall destruction, and collapse of small airways
• COVID-19 causes oedema, inflammatory vascular injury, pneumocyte type II hyperplasia, intra-alveolar giant cells, fibrin deposits, hyaline membrane formation, thrombosis, and fibrosis