Airways and Lungs Sanjaya Adikari Department of Anatomy

Nasal Cavity Nasopharynx (Oropharynx) Larynx Trachea Bronchi ………. Upper respiratory tract Lower respiratory tract

Trachea Primary bronchi Secondary bronchi Tertiary bronchi Bronchioles Terminal bronchioles Respiratory bronchioles Alveolar ducts Alveolar sacs Alveoli L & R bronchi Lobar bronchi Segmental bronchi

Nasal cavity Hair at the entrance to trap bigger particles Mucous and serous glands to produce secretions to trap smaller particles and moisturize the air Highly vascular to increase air temperature Folds on the nasal walls to increase the surface area Pseudostratified columnar ciliated epithelium which traps and moves up the dust particles

General histological arrangement of the airway Mucosa Smooth muscle layer Submucosa Cartilage layer Adventitia

Changes in the arrangement PSCC epithelium in large air ways become simple cuboidal nonciliated epithelium in small air ways Frequently seen goblet cells become less frequent and totally absent in terminal bronchioles The layer of smooth muscles becomes thicker as it goes down and becomes maximum at terminal bronchioles Serous and mucous glands in submucosal connective tissue becomes less numerous and absent beyond tertiary bronchi Cartilage parts smaller in small airways

Trachea Pseudostratified columnar ciliated epithelium Smooth muscle layer almost absent Numerous serous mucous glands in the submucosa 'C' shaped hyaline cartilage

Primary and secondary bronchi Less taller respiratory epithelium Smooth muscle layer discontinuous Fewer serous and mucous glands Few hyaline cartilage plates rather than 'C' shaped ones

Tertiary bronchi Tall simple columnar ciliated epithelium Smooth muscle layer continuous Very fewer serous and mucous glands Few small irregular hyaline cartilage plates

Bronchioles Airways < 1 mm in diameter Simple columnar ciliated epithelium Smooth muscle layer continuous and prominent Serous and mucous glands absent Cartilage plates absent

Terminal bronchioles Structure is as same as the other bronchioles End of the purely conducting portion of the airway Respiratory bronchioles Walls contain small number of single alveoli Ciliated cuboidal epithelium. No goblet cells

Alveolar ducts Numerous alveolar sacs open into these Simple cuboidal nonciliated epithelium

Alveolar wall Type I pneumocytes (The squamous cells) –Forms part of the gaseous diffusion barrier Type II pneumocytes –Produce surfactant Connective tissue –Reticulin, collagen and elastic fibres with fibroblasts. –Macrophages. Blood vessels, mainly capillaries

Respiratory barrier/Gaseous diffusion barrier Type I pneumocyte Common BM Capillary endothelial cell

Alveolar pores Equalize the pressure between the alveoli Collateral circulation of air when the bronchiole is obstructed Responsible for easy spread of infection eg. Lobar pneumonia

Pleura