DIGESTION 187 



The epithelial secreting cells consist of granular protoplasm containing a well- 

 defined nucleus. The intestinal follicles constitute the apparatus which secretes 

 the chief portion of the intestinal juice. 



The surface of the mucous membrane presents throughout its entire extent 

 fine filiform or conical processes termed villi. The structure and function of the 

 villi will be considered in connection with the absorption of food materials. 



The pancreas and liver are developed, during embryonic life, from the walls of 

 the intestine and are anatomically and physiologically associated with it. 



PANCREAS 



The Pancreas. This gland is long, narrow and flattened and is situated 

 deep in the abdominal cavity, lying just behind the stomach. It measures 

 from fifteen to twenty centimeters in length, six in breadth, and two and a 

 half in thickness. It is usually divided into a head, body, and tail. The 

 head is directed to the right side and is embraced by the curved portion of the 



Pancreatic ducts. Common bile-duct- 



Tail. 



FIG. 77. PANCREAS AND DUODENUM REMOVED FROM THE BODY AND SEEN FROM BEHIND. 

 THE GLAND is CUT TO SHOW THE DUCTS. (Landois and Stirling.) 



duodenum; the tail is directed to the left side and extends as far as the spleen 

 (Fig. 77). The pancreas communicates with the intestine by means of a 

 duct. This duct commences at the tail and runs transversely through the 

 body of the gland. As it approaches the head of the gland it gradually in- 

 creases in size until it measures about two or three millimeters in diameter. 

 It then curves downward and forward and opens into, the duodenum. In 

 its course through the gland it receives branches which enter it nearly at 

 right angles. The pancreas is richly supplied with blood-vessels and nerves, 

 the latter coming from the vagus nerve and semilunar ganglion. 



Histologic Structure. In its structure the pancreas resembles the 

 salivary glands. It consists of a connective-tissue framework which divides 

 the gland tissue into lobules. Each lobule is composed of a number of 

 acini or alveoli, more or less elongated or tubular in shape. Each acinus 

 gives origin to a small duct which, unit'ng with adjoining ducts, forms the 

 lobular duct, which becomes tributary to the main duct. The acinus is 

 lined by a layer of cylindric epithelial cells characterized by a difference 

 in structure between their central and peripheral ends (Fig. 78). The 

 central end, that bordering the lumen of the acinus, is dark in appear- 

 ance and filled with dark granules, while the peripheral end is clear and 

 homogeneous. The relative depth of these two zones varies according 



