CHAPTER XVII 



THE RESPIRATORY SYSTEM 



The respiratory apparatus consists of a system of passages — nares, 

 larynx, trachea, and bronchi, which serve for the transmission of air 

 to and from the essential organ of respiration, the lungs. 



The Nares 



The nares, or nasal passages, are divided into vestibular, respira- 

 tory, and olfactory regions, the differentiation depending mainly upon 

 the structure of their mucous membranes. 



The VESTIBULAR REGION marks the transition between skin and 

 mucous membrane (page 225). Its epithelium is of the stratified 

 squamous variety and rests upon a basement membrane, which is 

 thrown into folds by papillae of the underlying stroma. The latter is 

 richly cellular, and contains sebaceous glands (page 397) and the fol- 

 Ucles of the nasal hairs. 



The RESPIRATORY REGION is much larger than both the vestibular 

 and olfactory regions. Its epithelium is of the stratified columnar 

 variety. The cells of the surface layer are ciHated and are inter- 

 spersed with goblet cells. The stroma is distinguished by its thick- 

 ness (3 to 5 mm. over the inferior turbinates) and by the presence of 

 networks of such large veins that the tissue closely resembles erectile 

 tissue. It contains considerable diffuse lymphoid tissue and here and 

 there small lymph nodules. In the stroma are small simple tubular 

 glands Hned with both serous and mucous cells. There is no sub- 

 mucosa, the stroma being connected directly with the periosteum and 

 perichondrium of the nasal bones and cartilages. 



The mucous membrane of the accessory nasal sinuses is similar in 

 structure to that of the respiratory region of the nares, but is thinner 

 and contains fewer glands. 



The OLFACTORY REGION can be distinguished with the naked eye 

 by its brownish-yellow color, in contrast with the reddish tint of the 

 surrounding respiratory mucosa. The epitheHum is of the stratified 

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