Airways and Lungs

Sanjaya AdikariDepartment of Anatomy

Nasal CavityNasopharynx (Oropharynx)

LarynxTrachea Bronchi……….

Upper respiratory tract

Lower respiratory tract

TracheaPrimary bronchi Secondary bronchi Tertiary bronchi Bronchioles Terminal bronchioles Respiratory bronchioles Alveolar ducts Alveolar sacsAlveoli

L & R bronchiLobar bronchiSegmental 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