DEPOSITION OF TRIGLYCERIDES AND PHOSPHOLIPIDS 



4. The Deposition of Triglycerides and Phospholipids 

 in the Tissues 



According to the general consensus of opinion, neutral fats have a com- 

 paratively brief stay in the blood and tissues before they become oxidized 

 or until they are incorporated into the depot fats. It has been suggested 

 that the newly-absorbed fats are first carried to the liver, where they are 

 worked over and remodeled to conform to the fatty acid pattern of the 

 storage fat of the particular animal involved. However, the fat depots 

 themselves must exert some power to modify the type of fat which they 

 store. Otherwise, all storage fats in any one animal would be identical, 

 and it is a well-known fact that there are marked variations in the physical 

 constants of the depot fats from different parts of the animal body. The 

 chief sites in which neutral fat is stored in the animal are in the muscle 

 (intramuscular), around the ovaries (ovarian or genital), under the skin 

 (subcutaneous), in the connective tissue around the kidney (perirenal), 

 around the heart (pericardial), in the mesentery (mesenteric), and in the 

 omentum (omental). This adipose tissue may contain as high a propor- 

 tion as 90% of neutral fat. Although lipids are present in eveiy organ of 

 the body, they do not consist primarily of neutral fats, but rather of phos- 

 pholipids, cholesterol, and cerebrosides. These latter lipids serve in these 

 organs as essential structural components. 



In the case of the non-herbivores, the depot fat originates, at least in 

 part, from the ingested fats. This is proved by the demonstration of the 

 presence of unusual fatty acids in the depot fats when fats containing non- 

 physiologic fatty acids are fed. This effect can be particularly noted when 

 the fat consumption is high. However, a considerable proportion of the 

 fat deposits may likewise originate from newly-synthesized fat derived 

 from carbohydrate, as well as from protein. It is believed that this is 

 the chief source of the body fat in ruminants. This fact explains the 

 relative constancy in the composition of the fat in this group of animals, 

 and the difficulty of influencing its composition as the result of diet. 

 Proof has been forthcoming that one site of synthesis of body fats from 

 carbohydrates may be in the adipose tissue itself. 



In addition to diet, a number of factors influence the site and quality 

 of the fat deposited in the several depots. These include the species of 

 the animal, age, sex, environmental temperature, and exercise. Fat 

 deposition is greatly altered l)y ovariectomj', or by the administration of 

 thyroxine. 



The fat stored in the adipose tissues represents a dynamically active 



