1132 



THE DIGESTIVE SYSTEM. 



The simplest form of this type of gland is a portion of an epithelial surface, 

 continuous with adjacent portions of the surface, but involuted from the surface 

 to which it originally belonged. 



The simplest form in which this involution occurs is as a single pocket, of uniform size 

 throughout, forming a simple tubular gland. Of this kind are the intestinal glands in the wall 

 of the small intestine. 



In other cases there may be a bag -like enlargement of the end of the gland, forming a sort of 

 pocket, called an alveolus (alveolus, small stomach or bag), and this type of gland is known as 

 the simple alveolar gland. It does not exist in the alimentary canal. 



In some cases the lower part or fundus of the gland does all the secretion, and the upper 

 part forms a tube or duct that carries the secretion to the surface. 



When the outgrowth forming the gland remains undivided, the gland is known 

 as a simple gland. It may, on the other hand, break up into two or more branches, 

 and it then is known as a compound gland, and this compound gland may be 

 tubular, alveolar, or of a mixed tubular and alveolar form. 



When the fundus of the gland at the extremities of the ducts becomes a 

 highly differentiated saccular region, consisting of several enlargements (alveoli) 



Small duct from an alveolus at tne end of a duct, 



Large duct ^ i /^O^jt^^^^^ it is called an acinus 



4 ** ^mm^ ( , Kl a or 



N ' O JL * 



grape-stone), from the 

 fancied resemblance it 

 presents to a cluster 

 of grapes at the end 



'^\^\^=^-/-' :G Jr<c * f^^Yl i^i r \KJKSEBf" of a stalk. A. gland 



I T L-LL-U5M formed of several such 



structures collected 

 together is of ten called 

 a compound acinous or 

 racemose gland (race- 

 mus, a cluster). 



Most of the glands j of 

 the body are examples of 

 this variety e.g. the sali- 

 vary glands, the small 

 glands of the mouth, 

 tongue, pharynx, ceso- 

 phagus, etc. 



A compound acinous 



should be noted. The relatively clear cells, with the dark crescents of (racemose) gland is com- 

 Gianuzzi, are distinctive in the mucous gland. posed of a main duct 



which branches and re- 

 branches more or less freely according to the size of the gland. The terminal divisions of the 

 ducts end finally in specialised secreting parts, the acini or alveoli, quite distinguishable from 

 the ducts or conducting parts. In typical acinous glands the acini or alveoli are distinctly saccular ; 

 in other glands, such as the pancreas, this is not the case, the acini being long and narrow. 

 Accordingly, the term alveolo- or acino-tubular has been introduced and applied to glands of this 

 latter type, which is usually made to include the pancreas, and Brunner's duodenal glands. 1 



It should be added that the term acino-tubular is by some authors used exclusively instead 

 of acinous for all racemose glands. 



The foregoing may be summarised in tabular form thus : 



I. Simple glands. Duct undivided. 



(a) Simple tubular (undilated at end) e.g. intestinal glands and certain gastric glands. 

 (6) Simple alveolar (dilated at end) not met with in alimentary canal. 



II. Compound glands. Duct divided. 



(a) Compound tubular, branched elongated tubes, no acini e.g. most gastric glands. 

 (6) Compound acinous or alveolar (racemose glands), branched duct with saccular acini or 

 terminal branches e.g. salivary glands ; the mucous glands of the mouth, tongue 

 palate, pharynx, and oesophagus. 



An alveolus with secreting cell 



Duct 



Crescent of Gianuzzi 



Connective tissue 



FIG. 895. SECTION OF A SEROUS GLAND ON THE LEFT, A Mucous GLAND 

 ON THE RIGHT SIDE (Bohm and v. Davidoff.) 



In the serous gland the granular secreting cells and the centrally -placed nucleus 



1 Some authorities consider the duodenal glands of Brunner to belong to the class of compound tubula 

 glands (Heidenhain, Watney, Jonnesco, etc.). 



