Lung
•The respiratory tree consists of trachea, bronchi, bronchioles, terminal bronchioles, respiratory bronchioles and alveoli. Parts distal to respiratory bronchioles are
involved in gas exchange
•Thin-walled alveoli lined by flat cells. Two types of cells lines the alveoli:
Type I pneumocytes-simple squamous cells
Type II pneumocytes-surfactant producing.
•Lumen also contains macrophages called as dust cells which phagocytose the dust particles.
•Bronchus lined by pseudostratified ciliated columnar epithelium with goblet cells
Irregular plates of hyaline cartilage present in the bronchial wall.
•Bronchioles are smaller in size, I mm or less.
Lined by simple ciliated columnar epithelium without goblet cells. Hyaline cartilage is absent in the wall. Has more smooth muscles and are prone for spasm.
•Respiratory lining epithelium changes to simple columnar at terminal broncnioles, cuboldal at respiratory bronchioles and squamous epithelium at alveoli.
•Blood Gas barrier is formed by alveolar simple squamous epithelhum with lts basenent membrane and capillary endothelium with its basement membrane.
Trachea
• Mucosa--lining epithelium is pseudostratified cilated columnar epitnelnum witn gotblet cells. Lies over thin layer of connective tissue called lamina propria.
•Cilia of pseudostratified ciliated columnar epithelium beat upward, so that mucus with trapped foreign particles are expelled.
•Goblet cells and glands of submucosa secret mucus which traps dust particles.
•Submucosa-Made of connective tissue with blood vessels and nerves.
Contains lot of serous and mucus glands. Elastic fibers are prominent.
•Cartilage-C-shaped hyaline cartilage gives firm, flexible wall and contour to trachea.
Posterior ends of cartilage connected by trachealis muscle which completes the lumen and allows esophageal expansion
• Adventitia-made of connective tissue with blood vessels.