308 



THE RESPIRATORY SYSTEM 



Each bronchiole enters the apex of a pulmonary lobule (secondary) and 

 divides into terminal so-called respiratory bronchioles (terminal bron- 

 chioles). 



Fia. 291. FROM A SECTION or A CHILD'S LUNG. 



B, bronchiole in transection, with its adjacent pulmonary artery, A; TB, bron- 

 chiole, ending in a terminal bronchiole, from which are derived the alveolar duct, 7, 

 the atrium, A, and the pulmonary alveoli, PA. In the center of the figure a pul- 

 monary alveolus, PA, is seen in transection; many similar ones are shown. Hema- 

 tein and eosin. Photo. X 45. 



The respiratory bronchiole bears alveoli which become more numer- 

 ous toward its distal end. It thus contains a variable epithelial lining 

 consisting proximally of a low columnar, sometimes ciliated, epithelium, 

 with distally a more flattened non-ciliated type, and in the alveoli a 

 typical greatly flattened respiratory epithelium including non-nucleated 



