The histology of Intrapulmonary bronchi is similar to that of the trachea and extra-pulmonary bronchiole, except that C-shaped cartilage rings are absent here and replaced by cartilage plates. Intrapulmonary Bronchus : Pseudo-stratified Columnar Ciliated Bronchial Epithelium Cartilage Plates & Seromucous Bronchial Glands Terminal Bronchiole : Simple Columnar Epithelium Prominent mucosal folds & well developed smooth muscles Respiratory Bronchiole : Simple Cuboidal Epithelium Alveolar Out-pocketings in the wall Gives rise to alveolar ducts Alveolar Walls : Out-pocketings of respiratory bronchioles type 1 & 2 Pneumocyets Also contain Alveolar macrophages Bands of Smooth muscle fibres in interalveolar septa