152 



II. DIGESTION AND ABSORPTION OF FATS 



solved into their separate components when an acid reaction obtains. 

 Although it has generally been considered that the reaction in the small 

 intestine is alkaline, more recent results have indicated that the contents 

 of the duodenum and jejunum have an acid reaction, 641 - 642 the pH averaging 

 about 6. .3. Although a more alkaline medium may exist in the lower ileum, 

 an emulsifying system, to be effective in the intestine, must be stable at a 

 pH of 6.5. 



Table 17 



Comparison of the Explanations for Changes Occurring in the Lumen of the 



Intestine as Postulated in the Lipolytic and Partition Theories' 1 



Lipolytic theory 



Partition theory 



Emulsification: 



1. Mechanism 



2. Function 



Hydrolysis: 



1. Extent 



2. End-products 



3. Function 



Acid soap 



To promote hydrolysis 



Complete 



Fatty acids and glycerol 



Essential preliminary to 

 absorption 



Triple combination: fatty acid/ 

 bile salt/lower glyceride 6 



To disperse unhydrolyzed fat 

 preparatory to absorption 



Partial 



Fatty acids, di- and monoglycer- 

 ides, and later glycerol* 



Provides 2/3 of components of 

 emulsifying system. Parti- 

 tions fall into fatty acid and 

 glyceride fractions 



«• A. C. Frazer, Physiol. Revs., 26. 103-119 (1946). 



b A. C. Frazer, J. H. Schulman, and H. C. Stewart, /. Physiol, 103, 306-31G (1944). 



« A. C. Frazer and H. G. Sammons, Biochem. J., 39, 122-128 (1945). 



Frazer 645 has analyzed possible mechanisms for promoting emulsification 

 which will function under the conditions listed above. Bile salts, some- 

 times considered to be the only essential requirement for producing an 

 emulsion, form only a crude emulsion, with low stability compared with 

 that known to exist in the lumen of the gut. In the second place, soap has 

 been considered as the component in the intestinal contents which renders 

 possible the production of a stable emulsion. 727 It is true that soap is an 

 excellent emulsifying agent in an alkaline solution, but it will not function 

 at a pH on the acid side of 7.5. It has been suggested that so-called "acid 

 soaps" cause emulsification, but Frazer 645 discounts the effectiveness of such 

 compounds, and indicates their complete ineffectiveness in the presence of 

 calcium. Although the presence of cholesterol may enhance the emulsify- 



727 J. Mcllanby, ./. Physiol., 64, vP-viP (1927). 



