296 ANATOMY FOR NURSES [Chap. XV 



fied form, and this action may be important in the digestion of milk 

 fat by infants, as the pancreas is inactive. 



CHANGES THE FOOD UNDERGOES IN THE SMALL 

 INTESTINE 



The ch^ine, on entering the duodenum, after an ordinary meal, 

 is a mixture of various matters. It contains some undigested 

 proteins ; some undigested starch ; oils from fats eaten ; peptones 

 formed in the stomach ; salines and sugars ; all mixed with a good 

 deal of water and the secretions of the alimentary canal. It is in 

 the intestines that this mixture undergoes the most profound diges- 

 tive changes. These changes which constitute intestinal digestion 

 are effected by : (1) the movements of the intestines, (2) the pan- 

 creatic juice, (3) the succus entericus or secretion of the intestinal 

 glands, and (4) the bile. 



Movements of the small intestine. — The movements of the 

 small intestine are of two kinds : (1) peristaltic and (2) rhythmic 

 segmentation, 



(1) A peristaltic movement may be defined as a quick succession 

 of waves of contraction and inhibition passing slowly along the 

 intestine and affecting the longitudinal fibres. The wave of 

 contraction begins at a certain point, passes downward away from 

 the stomach, and is always preceded by an area of inhibition or 

 relaxation. The purpose of it is to pass the food slowly forward, 

 and it is obvious that the wave of contraction is more effective in 

 forcing the contents forward because just in front of it the intes- 

 tine is relaxed. 



(2) The movements of rhythmic segmentation consist of 

 contractions of the circular fibres of the intestine, which occur at 

 the same time as the contractions of the longitudinal fibres. The 

 purpose of these contractions is to split the column of food into a 

 number of equal segments. Within a few seconds each of these 

 segments is halved and the corresponding halves of adjoining 

 segments unite. Again contractions recur and these newly formed 

 segments are divided, and the halves re-form in the same position 

 as they had at first. In this way every particle of food is brought 

 into intimate contact with the vahiilre conniventes and is 

 thoroughly mixed with the digestive juices. 



Secretion of pancreatic juice. — Just as chewing and swallowing 



