PROBLEM 2 



Fig. 204 The stomach and 

 the upper end of the small 

 intestine. Note especially the 

 mucous lining and the mus- 

 cle layers in the stomach. 

 How do bile and pancreatic 

 juice get into the intestine? 



The Digestive System Makes Food Usable 



Oesophagus ^,- 

 Pancreatic ducts 

 Bile duct 



195 



Gall bl 



omall 

 intestine 



Opening 

 of bile and 

 pancreatic ducts 



Stomach there is a different epithehal tis- 

 sue called mucous membrane. This con- 

 sists of several layers of epithelial cells 

 laid on a foundation of connective tissue. 

 The epithelial cells secrete mucus. When 

 a large amount of mucus has accumulated 

 each cell is shaped like a flask and for 

 this reason these cells are called goblet 

 cells. Finally the cell bursts and the mu- 

 cus is discharged. Figure 228 on page 

 227 shows two goblet cells discharging. 

 Scattered through this mucous layer are 

 the microscopic glands that secrete gas- 

 tric juice. These are sunk into the thick 

 wall of the stomach. These glands are 

 made of epithelial cells of various kinds. 

 Blood vessels and the fibers of nerve cells 

 run through and between all these many 

 kinds of tissues. Thus, in this one organ 

 are found examples of all the different 

 kinds of animal tissues except bone and 

 cartilage. 



Stomach movements. When the food 

 reaches the stomach much of it is still 

 in large pieces even if it has been well 

 chewed. During the two to four hours 

 that the food mass remains in the stomach 

 it is moved back and forth and around. 



Oblique 

 Circular 

 Longitudinal 



V 



Stomach 



,, ,. . muscle fibers 



Mucous Immg 



As the sets of muscles contract and relax 

 in turn, the stomach goes through several 

 kinds of movements but only some of 

 these movements are of the type that 

 move the food onward. The churning 

 movements break up the pieces of food 

 still further and mix them thoroughly 

 with the gastric juice. The importance of 

 these regular muscular contractions is 

 now recognized. Many of our digestive 

 disorders are the result of the improper 

 action of the muscular walls. By doing 

 Exercise 16, you can demonstrate the 

 importance of the mechanical breaking 

 up of food. 



While stomach movements and diges- 

 tion continue, the rings of muscle at each 

 end of the stomach are more or less 

 contracted. Only liquids can pass through 

 the ring into the small intestine. What- 

 ever liquid food you eat passes on al- 

 most immediately after its arrival in the 

 stomach. After a while when digestion 

 has been going on for some time a ring 

 of muscle (the pyloric sphincter) be- 

 tween the stomach and intestine relaxes 

 more. As the softened and well-broken- 

 up portions of food are pushed forward 



