THE PANCREAS 



183 



ends of the secreting cells. I'hese cells represent a contiiuiation 

 of the intercalated dncts which project a short way into the acinar 

 lumen. Such cells have no secretory granules and possess a small 

 deeply staining nucleus. Intercalated ducts hned with first cuhoidal 

 then low cohnnnar pass to small excretory ducts lined with a tall 

 columnar epithelium. The large excretory ducts are lined with 

 a stratified columnar epithelium and pass into the main duct (duct 

 of Wirsung), which opens into the intestinal lumen. Enzymes 

 (trypsin, amylase, and lipase) present in the pancreatic secretion 

 break down the proteins, starches, and fats into simpler compounds. 



Fig. 11!S. — Section of pancreas of the water snake (Natrix>. It is similar to the 

 pancreas of a mammal but relatively less connective tissue makes it more compactly 

 glandular. The light gray areas are sections of islands of Langerhans. 



Though at first glance it resembles the parotid of manunals, the 

 pancreas difl'ers in the nature of its secretory cells, in the looser 

 arrangement of the interlobular connective tissue, in the absence 

 of secretory ducts, and finally in the i)resence of certain groups of 

 very distinct lightly staining cells forming the islands of Langerhans. 



The islands of Langerhans are composed of s])herical groups of 

 from few to hundreds of lightly staining cells irregularly scattered 

 among the acini and along the ducts. (Fig. US.) These cells are 

 arranged in cords forming a network with munerous wide capillaries 

 passing between the cords. Two types of cells are demonstrated on 

 the basis of secretory granules which are not in either case like those 

 of the acinar cells of the pancreas. One, the A cell, with fine 



