46 HISTOLOGY. 



Glandular Epithelium and Glands. 



Glands consist almost exclusively of epithelial tissue. In 

 every case the most important i. e., the secreting elements 

 are epithelial cells. We must therefore speak here in connec- 

 tion with epithelial tissues of the structure and classification of 

 glands. 



Glandular epithelium is one possessing a secretory function. 

 By secretion we mean the production and elimination of mate- 

 rials which are not to be used directly in the building up of the 

 body. These products may be made use of by the organism, in 

 which case the process is called secretion. If, however, the 

 materials eliminated are waste products, and of no value to the 

 body, the process is one of excretion. If the latter are retained 

 by the organism, they may be a menace to its welfare. These 

 glandular functions may be carried out by a single cell, in which 

 instance we have a unicellular gland; or there may be many 

 cells combined to form what is known as a multicellular or true 

 gland. 



As an example of unicellular glands, we have the so- 

 called goblet cells, which were described especially as a modi- 

 fication of the cylindrical epithelial cell. They produce 

 mucus from their protoplasm (Fig. 22), and consist of two 

 parts : a lower plasmatic portion, containing the nucleus ; and 

 the upper part near the surface of the epithelium, consist- 

 ing of mucus. If this is present in large quantities, the upper 

 part of the cell becomes dilated or swollen, so that the whole 

 may with some truth be compared with a goblet. The basal 

 part of the cell usually remains thin, and often is drawn to a 

 point. Even ciliated epithelium, or that with a striated border, 

 is capable of producing mucus and giving rise to goblet cells. 

 The change always begins in the free end of the cell by the pro- 

 duction of small bright globules, which increase in size, flow to- 

 ucther, and finally leave only a small quantity of unchanged pro- 

 toplasm as a sort of framework to hold the mucus. At the same 

 time there is formed on the surface a cell membrane which pre- 

 vents the escape of the secretion. The nucleus finally is crowded 



