SECRETING GLANDS 



187 



This physiologic classification is not in any way the equivalent 

 of the histologic gland types mentioned above. Thus both serous 

 and mucous glands, in different locations, form almost every 

 variety of tubular gland. 



The glands of the fourth type are too varied in their structure 

 to be considered collectively to advantage. The reader is referred 

 to the several chapters in which they are described in detail. This 

 type includes the testis, the prostate, the ceruminous glands, many 

 of the ductless glands, and also some authors describe the ovary 

 and the lungs as conforming to the glandular type of structure. 



The mixed secreting glands include some tubules which are 

 characteristically mucous, while others are typical serous secreting. 

 Occasionally both types of secreting cells are contained within 

 the same tubule. 



Mucous secreting cells possess the general characteristics which 

 have been previously recited under the head of goblet cells (Chap- 

 ter II). When void of secretion the cytoplasm of mucous cells is 

 granular, their nucleus centrally situated, and their shape more or 

 less columnar. The pre-secretion accumulates in the central por- 

 tion of the cell and occupies an area, adjacent to the glandular 

 lumen, which steadily increases in size until the greater part of 

 the cytoplasm has been 

 replaced; the nucleus 

 is pushed to the distal 

 or attached end of the 

 cell; and the whole 

 cell often becomes 

 swollen and distended 

 to more than double its 

 original size. Finally 

 the cell membrane rup- 

 tures and the mucus 

 pours out upon the 

 free surface of the 

 membrane. 



At the base of the 

 mucous secreting cells, 

 and between them and 

 their basement mem- 

 brane, are groups of epithelial cells having a finely granular cyto- 

 plasm, which form crescentic cell masses, the demilunes of Heiden- 



Fio. 171. TRANSECTION OF THREE SECRETING rnu I.KS 



OF THE 8UBMAXILLARY GLAND OF MAN. 



A, a serous tubule ; B^ a mucous tubule ; (7, a mu- 

 cous tubule with a demilune, rf. Ik-mati-in and eosin. 

 x 665. 



