HISTOLOGY 



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Each lobe receives, at its hilus, a branch from one of the two main 

 bronchi. These branch repeatedly, gradually diminishing in size. The 

 large bronchi of the lung are Uned by pseudostratified ciliated columnar 

 epithelial cells, among which goblet cells are present in varying number. 

 The lamina propria consists of fibrous connective tissue containing elastic 

 fibers. The mucous membrane forms longitudinal folds. Beneath this 



Branch of pulmonary 

 vein 



Bronchium 



Artery 



membrane delicate smooth muscle fibers complete the wall. The bronchial 

 tubes of the lung do not contain any cartilage. In the smaller bronchi the 

 epithelial lining is simple columnar and ciliated. Short terminal bronchioles 

 are formed by the division of the smaller bronchi and are lined by low 

 columnar cells, cilia and goblet cells being absent. 



The terminal bronchioles give rise to respirator}- bronchioles, each of 

 which in turn forms several alveolar ducts. Alveolar sacs, containing 

 several alveoli, open from the alveolar ducts and form intercommunicating 

 spaces separated from each other by thin walled septa in which capillaries 

 anastomose. The respiratory bronchioles are lined by cuboidal epithelial 

 cells, which are surrounded by connective tissue containing elastic and 



