Energy triacylglycerol

Triacylglycerols Are a Major Form of Stored Energy in Animals... 

Triacylglycerols are the major energy-storing lipids, whereas phosphoglycerols, sphingomyelin, and gly-cosphingolipids are amphipathic and have structural functions in cell membranes as well as other specialized roles. 

Free fatty acids are removed from the blood extremely rapidly and oxidized (fulfilling 25-50% of energy requirements in starvation) or esterified to form triacylglycerol in the tissues. In starvation, esterified lipids from the circulation or in the tissues are oxidized as well, particularly in heart and skeletal muscle cells, where considerable stores of lipid are to be found. 

Catabolism The breakdown of complex molecules to simpler ones to yield energy (e.g., triacylglycerols to fatty acids) and the inactivation of physiologically active molecules (e.g., acetylcholine to choline and acetic acid). 

Adipose tissue This is a specialised connective tissue that stores much of the energy reserve of the body in the form of fat (triacylglycerol) within the cells, known as adipocytes, which are close packed within the connective tissue. Adipose tissue is located in a number of anatomically distinct deposits in the body, e.g. below the skin, around major organs and between muscles. 

The hormone leptin, which is secreted by adipose tissue, is considered to play a role in the control of the amount of triacylglycerol in adipose tissue by decreasing appetite and by increasing energy expenditure. Leptin increases the rate of the triacylglycerol fatty acid cycle (Chapter 15). 

In developed conntries, fat provides about 40% of the total energy consnmed but in some individuals this percentage may be mnch higher. Almost all of this is in the form of triacylglycerol, containing mainly long-chain bnt also some short-chain fatty acids. The stractnre, digestion, absorption and eventual fate of the products of absorption are described in Chapters 4 and 5 and the metabolism of fat is discussed in Chapter 7. 

In addition to the increased mobilisation of fatty acids, there is an increase in the rates of cycling in the intra- and inter-cellular triacylglycerol/fatty acid cycles that contribute to increased energy expenditure in trauma. 

Substrate cycling (e.g. the Cori cycle and the intra- and inter-cellular triacylglycerol/fatty acid cycles (Chapter 3)) in which there is no net metabolic change so that the energy from ATP hydrolysis is released as heat. 

Several processes contribute to the loss of weight loss of triacylglycerol in adipose tissue loss of protein in muscle hypermetabolism (increased energy expenditure, due to the... 

Fat metabolism in adipose tissue (top). Fats (triacylglycerols) are the most important energy reserve in the animal organism. They are mostly stored in insoluble form in the cells of adipose tissue—the adipocytes—where they are constantly being synthesized and broken down again. 

Synthesis of fatty acids and their incorporation into triacylglycerols are stimulated during this time of energy excess. 

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