Histomorphological studies of the bronchioles of yak (Bos grunniens)

The study was conducted to elucidate the histomorphological features of various bronchioles in the lungs of yak. The large bronchioles had folded mucosa, supported by muscularis mucosae. The lamina epithelialis had a thin pseudo-stratified ciliated columnar epithelium with few goblet cells. The number of ciliated columnar cells was reduced, while that of the non-ciliated short columnar. 'Clara' cells was increased towards the distal terminal bronchioles. The large bronchioles gave off 2-3 generations of terminal bronchioles, which ultimately produced 3-5 generations of respiratory bronchioles. The respiratory bronchioles were distinct and less wide having more number of cuboidal cells and less number of 'Clara' cells. The distal respiratory bronchioles gave off 2-4 generations of alveolar ducts, which continued with the alveolar sacs in the lung. The ducts and sacs were lined by low cuboidal to squamous epithelium. The interalveolar space was wider with abundant septal cells.