CHAPTER XV 

 GLANDS 



General Structure and Classification 



Attention was called in describing the functional activities of 

 cells (page 51) to the fact that certain cells possess the power of not 

 only carrying on the nutritive functions necessary to maintain their 

 own existence, but also of elaborating certain products either neces- 

 sary for the general body functions (secretions) or for the body to 

 eliminate as waste (excretions). Such cells are known as gland cells 

 or glandular epithelium, and an aggregation of these cells to form a 

 delinite structure for the purpose of carrying on secretion or excretion 

 is known as a gland. 



A gland may consist of a single cell, as, e.g., the mucous or goblet 

 cell on the free surface of a mucous membrane, or the unicellular 

 glands of invertebrates. Such a cell undergoes certain changes which 

 result in the production within itself of a substance which is to 

 be used outside the cell. The appearance which this cell presents 

 depends upon the stage of secretion. It is thus possible to differen- 

 tiate between a "resting' ' and an " active " cell or between an "empty " 

 and a "loaded" cell. The mucous secreting cell of the intestine is 

 one of the simple columnar cells which constitute the epithelium of the 

 mucous membrane. It is distinguishable as a mucous or goblet cell 

 only after secretion begins. The resting cell is granular and takes 

 a rather dark cytoplasmic stain. As the cell becomes active, part of 

 the cytoplasm is transformed into, or is replaced by, a clear substance 

 which does not stain Hke cytoplasm, but reacts to hasmatoxylin. 

 The mucus collects first in the free end of the cell, and gradually 

 increases in amount until the entire cell is filled, with the exception of 

 a small area at the base, where a little unchanged protoplasm sur- 

 rounds a flattened nucleus. The cell at this stage is much larger than 

 in the resting state, and finally ruptures on the free surface and pours 

 out its secretion. Opinions difi'er as to the further behavior of this 

 cell. According to some, its life history is now ended, and its place is 

 taken by other cells which pass through the same process. Others 



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