CHAPTER XXXIV 



DIGESTION IN THE INTESTINES 



HERE we have to consider the action of pancreatic juice, of bile, and of 

 the succus entericus. 



The Pancreas. 



This is a tubulo-racemose gland closely resembling the salivary 

 glands in structure. The principal differences are that the alveoli or 

 acini are more tubular in character ; 

 the connective tissue between them 

 is looser, and in it are small 

 groups of epithelium cells (islets of 

 Langerhans) which are supplied by a 

 close network of capillaries (fig. 359). 



The secreting cells of the 

 pancreas are polyhedral. When 

 examined in the fresh condition, or 

 in preparations preserved by osmic 

 acid, their protoplasm is seen to be 

 filled in the inner two-thirds with 

 small granules ; but the outer third 

 is left clear, and stains readily with 

 protoplasmic dyes (fig. 358). 



During secretion the granules are 

 discharged ; the clear zone conse- 

 quently becomes wider, and the 

 granular zone narrower. 



These granules indicate the 

 presence of a zymogen or more 



probably of a mixture of zymogens, the precursors of the enzymes in 

 the juice. 



In the centre of the acini, spindle-shaped cells (centro-acinar cells) 

 are often seen ; their function and origin are unknown. 



517 



FIG. 35S. Section of the pancreas of a dog 

 during digestion, a, Alveoli lined with 

 cells, the clear outer zone of which is well 

 stained with haematoxylin ; d, duct lined 

 with short cubical cells, x 350. (Klein 

 and Noble Smith.) 



