MOVEMENTS OF THE STOMACH 283 



4. MOVEMENTS OF THE STOMACH 



A. KNEADING MOVEMENTS 



The purpose accomplished by the movements of the stomach is to mix 

 the food with the gastric juice and to reduce it mechanically by kneading 

 and grinding. By this means the chemical changes to be wrought by the 

 gastric juice are aided materially. The digestion of proteid in an artificial 

 gastric juice requires much less time if the proteid is kept moving than if it 

 is allowed to remain quiet. The proteid is more accessible to the gastric juice 

 by reason of the movement, and the kneading, such as takes place in natural 

 digestion, easily reduces to small pieces the masses already rendered brittle 

 by the preliminary effect of the gastric juice. 



With reference to the musculature of the stomach, we have to distinguish 

 the two openings, the cardia and pylorus, as well as the main body or fundus, 

 and the antrum pylori. The openings are surrounded by strong muscular fibers 

 and are as a rule closed. The fundus, or body of the stomach, has a relatively 

 weak musculature, the antrum a very strong one. 



Observations on the movements of the stomach after the ingestion of food 

 all agree in finding the contractions of the pyloric portion much more powerful 

 than those of the body of the stomach. The former is marked off from the 

 fundus by a ring muscle called the sphincter of the antrum. Relatively weak 

 peristaltic waves sweep over the .fundus from the cardiac end, and are con- 

 tinued by the very powerful contractions of the antrum, beginning at the 

 sphincter of the antrum and spreading toward the pylorus. 



Meltzer found that the fundic portion does not respond, even to very strong 

 stimulation with easily recognizable contractions, whereas the pyloric portion 

 with the same stimulus contracts more energetically the closer the stimulus is 

 applied to the pylorus itself. 



In a patient with a stomach fistula, a pressure of 14 to 35 mm. Hg. has been 

 observed in the body of the stomach, and 130 mm. in the antrum. The antrum, 

 it seems, may be closed off completely by contraction of its sphincter or by local 

 contractions of separate sections, from the parts of the stomach lying to the left. 



Since the pressure exerted by the fundic wall is commonly not very strong 

 .and the antrum is filled therefore during the dilatation which follows its own 

 contractions under, a very weak vis a tergo, the coarser portions of the food 

 are probably not pressed into the antrum, but only the easily mobile, more 

 fluid and more gruelly portions. If this is true, it follows further that the 

 changes which the food undergoes in the body of the stomach are principally 

 of a chemical nature, while the antrum represents the truly motor part of 

 the stomach, where the bits of food already more or less comminuted are 

 intimately mixed with the gastric juice and still more thoroughly ground up 

 by powerful .contractions. 



Experiment shows that the stomach, deprived entirely of nerves, or even 

 cut out of the body, undergoes spontaneous contractions', that like the heart, 

 the stomach has. therefore, within itself all the necessary conditions of its 

 movements which is probably due to the ganglion cells found in the stomach 



