142 II. DIGESTION AND ABSORPTION OF FATS 



It may be attributed in part to the decreased surface tension which ob- 

 tains in the aqueous phase; such a phenomenon would likewise cause a 

 lowering of the interfacial tension between the aqueous and the oily phases. 

 When this occurs, the formation of emulsions is favored, and the solution 

 of one phase in the other is facilitated. 



Verzar and McDougall 654 suggested that the bile salts act as hydrotropic 

 agents to bring water-insoluble fatty acids into solution. These workers 

 were able to demonstrate that fatty acids could be brought into a soluble 

 and even into a diffusible form in vitro in acid solution when bile salts were 

 present in the medium. The possible mechanism for accomplishing this 

 condition is the formation of water-soluble bile salt + fatty acid complexes 

 known as "choleic acids"; these complexes are carried into the epithelial 

 cells, where they are broken down. For a discussion of the circulation of 

 bile salts, see page 111. Although these choleic acid complexes are readily 

 demonstrable in the case of the fatty acids, their formation with mono-, 

 di-, and triglycerides has not been proved in vitro. However, it is quite 

 probable that such coordination compounds might occur in vivo, since the 

 acholic portion of the choleic acids varies considerably in composition. 

 Thus, it would seem possible that this mechanism might be an essential 

 part of the absorption cycle, whether the fatty acids or the glycerides 

 themselves are the components transported into the epithelial cells. 



7. The Absorption and Transport of Fats 



(1) The Absorption of Fats from the Gastrointestinal Tract 



a. Introduction. After the hydrolysis of fat has proceeded to the di- 

 and monoglyceride stage or, according to the Bloor- Verzar theory, to glyc- 

 erol and fatty acids, absorption of these intermediates occurs. It has 

 long been known that the split products of the triglyceride molecule are 

 readily absorbable. The fact that mono- and diglycerides are either ab- 

 sorbed as such or after hydrolysis is shown by the complete utilization of 

 these compounds. 693-665 



Proof that the glycerol moiety is absorbable has been afforded by the 

 results reported by a number of workers. Thus it has been noted 666 ~ 669 

 that ingested glycerol reduces the ketonuria in fasting or diabetic men. 



663 H. C. Tidwell, /. Biol. Chem., 182, 405-414 (1950). 



664 W. Q. Braun and C. L. Shrewsbury, Oil and Soap, 18, 249-250 (1941). 



666 J. R. Ames, M. P. O'Grady, N. D. Embree, and P. L. Harris, J. Amer. Oil Chemists' 

 Soc, 28, 31-33 (1951). 



686 F. Hirschfeld, Z. klin. Med., 28, 176-209 (1895). 



667 G. Satta, Beitr. chem. Physiol. Pathol, 6, 376-391 (1905). 

 688 R. M. Lang, Biochem. J., 9, 456-478 (1915). 



889 H. M. Thomas, Bull. Johns Hopkins Hosp., 35, 201-206 (1924). 



