2Q8 



ESSENTIALS OF PHYSIOLOGY. 



THE CHANGES WHICH ACCOMPANY SECRETION 

 IN THE SALIVAEY GLANDS. 



(1) It has already been pointed out that a temporary diminution in 

 the volume of the gland follows stimulation of the secretory nerve. 

 This is followed by an expansion due to the dilatation of the blood- 

 vessels. Further, secretion is accompanied by histological changes and 

 by an alteration in electrical potential. 



(2) Histologically the salivary glands are of two types serous glands, 

 which produce a fluid containing proteins and ptyalin, and mucous 

 glands, the secretion of which contains mucin. The salivary glands of 

 the dog, however, secrete no ptyalin. The parotid in man and most 

 animals belongs to the serous type ; the submaxillary and sublingual are 



generally mucous, but the former is 

 serous in the rabbit and mixed in 

 man. The general structure of a 

 salivary gland is of the compound 

 acinous type, each acinus being 

 lined by columnar or cubical cells, 

 and the whole being held together 

 by connective tissue. 



If a portion of a mucous gland, 

 which is in the resting condition, be 

 teased in 2 per cent, salt solution, 

 FIG. 117. Mucous cells from fresh sub- the individual cells are seen to be 



maxillary glands of the dog. (Lang- somewhat columnar in shape and to 



ley.) From Schafer s Essentials of 



Histology. be filled with large granules which 



a, from a resting or loaded gland ; 6, from a swe ll up an d disintegrate On the 

 gland which has been secreting for some ^ 



time ; a', b', similar cells which have been addition of acetic acid. If the 

 treated with dilute acid. ,-,111 j i i i 



gland be hardened in alcohol and 



stained sections be examined, no granules are visible, but the body of 

 the cell is clear, with a delicate network, and the nucleus is flat and 

 lies at the base of the cell. In the case of a gland which has been 

 made to secrete profusely, either by means of electrical stimulation 

 or by the administration of pilocarpine, the granules are fewer in 

 number and are found in the part of the cell which abuts on the 

 lumen of the acinus ; and the cell is smaller than that in the resting 

 condition (fig. 117). The hardened specimen shows a larger propor- 

 tion of protoplasm, and the nucleus does not lie so close to the base 

 of the cell. In the process of secretion, therefore, there has been 

 a discharge of the granules contained in the cell. But from their 

 behaviour to reagents it is clear that the granules do not represent the 



