34 



VETERINARY PHYSIOLOGY 



Among these occur some larger, somewhat pear-shaped, 

 cells, attached by their small extremity. Their protoplasm 

 is collected at their point of attachment, while the body of the 

 cell is filled with mucin, a clear, transparent material. These 

 chalice cells producing mucin lead to the study of the next 

 type of epithelium. 



3. Secreting Epithelium. — This type of epithelium, 

 which has as its function the production of some material 

 which is to be excreted from the cell, is generally arranged 

 as the lining of depressions or pits — the glands. 



The simplest form of gland is the sivvple tuhular — a test- 

 tube-like depression, lined by secreting cells. Instead of being 

 simple, the tube may be branched, when the gland is described 



Fig. 7. — A Zymin-secreting Gland, to show an acinus lined by secreting 

 cells containing zj'mogen granules, and the duct. 



as racemose. In many glands the secreting epithelium is 

 confined to the deeper part of the tube, acinus (fig. 7), while 

 the more superficial part is lined by cells which do not 

 secrete, forming the duct. 



In many situations several simple glands are grouped 

 together, their ducts opening into one common duct, and a 

 compound gland results. 



Secreting epithelium varies according to the material it 

 produces. 



(A) Mucin-secreting Epithelium. — Many glands have for 

 their function the production of mucus, a slimy substance of 

 use in lubricating the mouth, stomach, intestine, etc. The 



