Fatty acids energy from

Fate of free fatty acids The free fatty acids derived from hydrolysis of triacylglycerol may directly enter adjacent mus cells or adipocytes. Alternatively, the free fatty acids may be tra ported in the blood in association with serum albumin until tt are taken up by cells. [Note Serum albumin is a large prot secreted by the liver. It transports a number of primarily hydropl bic compounds in the circulation, including free fatty acids a some drugs.2] Most cells can oxidize fatty acids to produ energy (see p. f88). Adipocytes can also reesterify free fa acids to produce triacylglycerol molecules, which are stored ui the fatty acids are needed by the body (see p. 185). 

The brain has no significant stores of triacylglycerol, and the oxidation of fatty acids obtained from blood makes little contribution to energy production because fatty acids do not efficiently cross the blood-brain barrier. The intertissue exchanges characteristic of the absorptive period are summarized in Figure 24.8. 

Increased fatty acid oxidation The oxidation of fatty acids derived from adipose tissue is the major source of energy in hepatic tis sue in the postabsorptive state (see Figure 24.11, ). 

Insulin is probably the most important inhibitor of lipolysis. In contrast to adults, in whom catecholamines represent the most important stimulators of lipolysis, thyrotropin (TSH) is the most important stimulator of lipolysis in the newborn. Plasma free fatty acid concentrations rise markedly in the first hours after birth in response to a marked increase in the TSH concentration and a fall in the insulin concentration. The fatty acids released from lipid stores are oxidized by some extrahepatic tissues (e.g., heart and skeletal muscle, kidney, intestine, and lung). Because the respiratory quotient (the ratio of carbon dioxide production to oxygen use) falls from a value of 1.0 (showing that carbohydrate oxidation is the primary source of energy) to a value of 0.8 to 0.9 (showing increasing oxidation of protein or fatty acids) at 2 to 12 hours of age, at a time when protein catabolism is usually insignificant, fatty acid oxidation must represent... 

Chylomicrons are produced from dietary fat by the removal of resynthesised triglycerides from the mucosal cells of the small intestine into the intestinal lumen. These then enter the circulation via the thoracic dncts in the lymphatic system and enter into the subclavian veins, where triglyceride content is reduced by the action of lipoprotein lipases (LPL) on capillary endothelial surfaces in skeletal muscle and fat. The free fatty acids (FFA) from the triglycerides are used by the tissues as an energy source or stored as triglycerides. The chylomicron remnants, stripped of triglyceride and therefore denser, are then taken up by the liver by LDL receptor-mediated endocytosis, thereby delivering cholesterol to the liver. 

FIGURE 4 8 Oxidation of carbohydrate and fatty adds for the production of energy. In the resting state, glycogen in the liver is broken down to glucose units however, both liver (kft) and muscle (right) derive most of their energy from fatty acids released from adipose tissue into the bloodstrecim and oxidized via the Krebs cycle. When carbohydrate is oxidized in the liver, it tends to be released into the bloodstream as pyruvate and lactate. 

The P-oxidation of fatty acids that occurs in the mitochondrial matrix provides the energy for gluconeogenesis in the liver. Fatty acids transported from adipose tissues by blood albumin cross the hepatic plasma membrane and... 

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