THE DIGESTIVE SYSTEM 



291 



The origin, structure, and function of these islands have been subjects of 

 much controversy. For some time they were considered of lymphoid origin. 

 They are now believed to be epithelial cells having a developmental history 

 similar to the cells lining the secreting tubules. Each cell-island consists of, 

 in addition to the cells, a tuft or glomerulus of broad tortuous anastomosing 

 capillaries, which arise from the network of capillaries surrounding the secret- 

 ing tubules. The close relation of cells and capillaries and the absence of any 

 ducts have led to the hypothesis that these cells furnish a secretion — internal 

 secretion — which passes directly into the blood-vessels. 



In a recent publication Opie reviews previous work upon the histology of the 

 pancreas and adds the results of his own careful researches. He concludes that 

 the cell-islands of Langerhans are definite structures "formed in embryological 



Fig. 193. — From Section of Pancreas, the blood-vessels of which had been injected 

 (Kiihne and Lea), showing island of Langerhans with injected blood-vessels, surrounded 

 by sections of tubules. Zymogen granules are distinct in inner ends of cells. 



life," that "they possess an anatomical identity as definite as the glomeruli of 

 the kidney or the Malpighian body of the spleen, and that they subserve some 

 special function." He calls attention to the similarity which Schafer noted 

 between these cell-islands and such small ductless structures as the carotid and 

 coccygeal glands and the parathyreoid bodies. From his study of the pancreas 

 in diabetes, Opie concludes that the islands of Langerhans are concerned in 

 carbohydrate metabolism. 



Blood-vessels. — The arteries enter the pancreas with the main 

 duct and break up into smaller arteries which accompany the smaller 

 ducts. These end in a capillary network among the secreting tubules. 

 From this, venous radicles arise which converge to form larger veins. 

 These pass out of the gland in company with the arteries. 



Lymphatics.^ — Of the lymphatics Httle is known. 



Nerves. — The nerves are almost wholly from the sympathetic 

 system, and are non-medullated. Some of them are axones of cells 

 in sympathetic ganglia, outside the pancreas; others, of cells situated 



