6 I. LIPID DIGESTION, ABSORPTION, TRANSPORT, AND STORAGE 



component. Although the quantity of fat so stored remains fairly con- 

 stant, it is now known that newly-absorbed fat, as well as newly-syn- 

 thesized fat, is constantly being added to the depots, where it replaces a 

 corresponding amount of fat which has been oxidized. It has been demon- 

 strated that, even in situations in which a negative caloric balance obtains, 

 some of the ingested fat is deposited in the adipose tissue, while a larger 

 part is lost by its transfer from the adipose tissue to other organs, where it 

 is oxidized. The reader is referred to Chapter VI (Volume II, The Lipids) 

 for general factors concerned with fat storage in the animal body. Chapter 

 VII of this earlier volume includes a review of the nature of the lipids 

 stored in the several organs. 



Under normal conditions phospholipids are not stored in the adipose 

 tissue. They do, however, make up an appreciable proportion of the lipid 

 in the intestinal wall, the liver, the kidney, and other organs. It is sup- 

 posed that they have a function in the structure of the cells of these organs, 

 and that they are concerned with intermediary metabolism and transport. 

 Plasma phospholipids appear to be entirely synthesized in the liver. In 

 such abnormal conditions as Niemann-Pick's disease, the deposition of 

 sphingomyelin occurs in the reticuloendothelial system and in most organs; 

 in another type of lipidosis, called Tay-Sachs' disease, the lipid deposited 

 in the tissues is a ganglioside. 



5. The Absorption, Transport, and Storage of 

 Cerebrosides and Hydrocarbons 



Little is knoAvn about the digestion and absorption of the cerebrosides. 

 Since the normal diet of man contains only negligible amounts of cere- 

 brosides, it is generally believed that the cerebrosides present in the tissues 

 originate in situ from the hydrolysis products rather than that they are 

 carried there from the intestinal tract. Moreover, since the cerebroside 

 molecule is readily hydrolyzed by lipases, it would seem probable that they 

 would not be absorbed without at least partial hydrolysis if they were 

 present in the diet. Definite quantities of cerebrosides are present in 

 the blood, but they are chiefly in the erythrocytes and leucocytes rather 

 than in the plasma. Cerebrosides are not stored in the adipose tissue. 

 Normally their main concentration is in the brain and spinal cord, al- 

 though the liver, spleen, and related organs contain small amounts. In 

 the abnormal condition known as Gaucher's disease or reticular and 

 histiocytic cerebrosidosis, cerebrosides are found in high concentrations 

 in the liver, and especially in the spleen and other parts of the reticulo- 



