EPITHELIAL TISSUES. 87 



3. GLANDULAR EPITHELIUM. 



Glandular eoithelium is composed of epithelial cells differen- 

 tiated so as to possess the power of elaborating certain compounds 

 or substances which are finally given off from the cells in the form 

 of secretions. Those substances which form the essential constitu- 

 ents of such secretions appear in the protoplasm of the majority of 

 glandular cells, in the intervals of secretory activity, in the form of 

 smaller and larger granules which may be discharged from the 

 cells in granular form or may be changed into homogeneous, viscid 

 substances before leaving or on leaving the cells. Glandular epi- 

 thelium appears in the form of isolated glandular cells, scattered 

 here and there among other epithelial cells, in certain types of epi- 

 thelium, or as smaller or larger aggregations of glandular cells, 

 possessing definite and typical arrangement and associated with 



Cilia 



Mucin. . 



Fig. 49. Goblet cells from the bronchus of a 

 dog. The middle cell still possesses its cilia. ; that to 

 the right has already emptied its mucous contents 

 (collapsed goblet cell) ; X 6 - 



Fig. 50. A mucus-secret- 

 ing cell (goblet cell), showing- 

 secretory granules, situated be- 

 tween two epithelial cells. 

 From the epithelium of the large 

 intestine of man. 



other tissues connective tissue, blood- and lymph-vessels, nerve 

 tissue to form structures or organs known as secreting glands. 



Unicellular Glands. Isolated glandular cells, which we may 

 know as unicellular glands, are frequently met with in the epithe- 

 lium of the intestinal canal and respiratory organs, where, owing to 

 their shape, they are known as goblet cells, or, again, as mucus 

 secreting cells, since their secretion is mucus. Such cells are in 

 the ordinary preparation distinguished from the neighboring cells 

 by the fact that their free ends appear clearer and are more vesicu- 

 lar, while their basal portions, containing the nuclei, are narrow 

 and pointed. Closer examination generally reveals a fine proto- 

 plasmic network in the clear portion of the cell, the interspaces of 

 which are filled with the mucus. (See Fig. 49.) 



The secretion is, however, elaborated in the cell-protoplasm in 



