CHAPTER III 



INNERVATION OF THE GLANDULAR 

 ELEMENTS 



Saliva may flow from a salivary gland because the secretory cells 

 have an inherent ability to secrete spontaneously or because they 

 are stimulated to activity by extracellular agents carried to the 

 gland by the blood or liberated from nerve endings. Examples of 

 spontaneous activity and of secretion induced by hormones will be 

 given in later chapters. The flow controlled by nerves, which is 

 undoubtedly the most important, will be considered in the present 

 chapter. 



In a discussion of the innervation of the salivary glands the 

 following complicating factors must be taken into account : 



i . The glands receive nerve fibres both from the parasympathetic 

 and the sympathetic nervous system. Both sets of nerves, electric- 

 ally stimulated, are able to affect the secretory process, but the 

 physiological significance of the double innervation of the glands 

 is not altogether clear. 



2. There is some uncertainty as to the route by which the nerves 

 reach some of the glands. Evidence suggests that secretory fibres 

 may arrive at some glands through unknown channels. This may 

 invalidate inferences drawn from denervation experiments. 



3. The saliva poured into the mouth results from activity in 

 different types of cells. It may be produced, for instance, both in 

 serous and mucous cells and its composition modified by the cells 

 of the ducts. An important problem, which has been the subject of 

 many investigations, is whether the single secretory cell is inner- 

 vated both by parasympathetic and sympathetic fibres. Little is 

 known about the innervation of the ducts. Histological and elec- 

 trical changes in their cells have been produced by stimulation of 

 nerves, but they may be indirect, due to activity evoked in the 

 secretory cells. On the other hand, the presence of true cholin- 

 esterase in the duct cells of the rat's submaxillary and sublingual 

 glands (Snell and Garrett, 1957) may suggest that these cells are 

 supplied with cholinergic nerve fibres. 



4. The nerves control structures in the glands other than the 



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