THE DIGKSTIVK SYSTEM 



287 



is much less distinct, although it can usually be made out. This is 

 due to the incompleteness of the connective-tissue septa, the human 

 pancreas in this respect resembling the human liver. Rarely the 

 human pancreas is distinctly lobulated. 



The gland has a main excretory duct, the pancreatic duct or duel 

 of Wirsting. In many cases there is also a secondary excretory duct, 

 the accessory pancreatic duct or duct of Santorini. Both open into 

 the duodenum. The main duct extends almost the entire length of 

 the gland, giving off short lateral branches, one of which enters the 

 centre of each lobule group. Here it splits up into branches which 

 pass to the primary lobules. From these intralobular ducts, are given 

 off long, narrow, intermediate tubules, which 

 in turn give rise to the terminal secreting 

 tubules (Fig. 187). 



The excretory ducts are lined with a simple 

 high columnar epithehum which rests upon 

 a basement membrane. Outside of this is a 

 connective-tissue coat, the thickness of which 

 is directly proportionate to the size of the 

 duct. In the pancreatic duct goblet cells are 

 present, and the accompanying connective 

 tissue of the main duct and of its larger 

 branches contains small mucous glands. As 

 the ducts decrease in size, the epithehum be- 

 comes lower until the intermediate tubule is 

 reached where it becomes flat. 



The terminal tubules themselves are most 

 of them very short, frequently almost spher- 

 ical. This and the fact that several terminal 

 tubules are given off from the end of each in- 

 termediate tubule have led to the description 

 of these tubules as alveoli, and of the pancreas 

 as a tuhulo-abeolar gland, although there is 

 no dilatation of the lumen. The terminal tubules are lined with an 

 irregularly conical epithelium resting upon a basement membrane 

 (Figs. 188 and 189). The appearance of these cells depends upon 

 their functional condition. Each cell consists of a central zone 

 bordering the lumen, which contains numerous granules known as 

 zymogen granules, and of a peripheral zone next to the basement 

 membrane, which is homogeneous and contains the nucleus (Fig. 



c 



Fig. 187. — Diagram to 

 illustrate Structure of Pan- 

 creas. (Stohr.) a, Excretory 

 duct; h, intermediate tubule; 

 c, c, terminal tubules. 



