Triacylglycerols glucose metabolism

Fig 9. Overview of the major pathways of glucose metabolism. Pathways for production of blood glucose are shown by dashed lines. FA = fatty acids TG = triacylglycerols OAA = oxaloacetate PEP = phosphoenolpyruvate UDP-G = UDP-glucose DHAP = dihydroxyacetone phosphate. 

Fig. 31.15. Glucose metabolism in various tissues. A. Effect of insulin on glycogen synthesis and degradation and on VLDL synthesis in the liver. B. Glucose metabolism in resting muscle in the fed state. The transport of glucose into cells and the synthesis of glycogen are stimulated by insulin. C. Glucose metabolism in adipose tissue in the fed state. FA = fatty acids DHAP = dihydroxyacetone phosphate. FA = fatty acids TG = triacylglycerols -I- = stimulated by insulin — = inhibited by insulin.

Figure 8.4 General summary of metabolism of amino adds. Amino adds in blood can be derived from the diet or hydrolysis of endogenous protein. The nitrogen in the amino acids can be used to synthesise other nitrogen-containing compounds (e.g. glutamine - see Table 8.4) or removed as urea (Chapter 10). The amino acids are also used to synthesise proteins or peptides. The carbon can be converted to CO2, glucose or triacylglycerol, but, in humans, very little is converted into fat, so triacylglycerol is omitted from the figure.

The major role of skeletal muscle is movement, which is described and discussed in Chapter 13). Nevertheless, since muscle comprises 40% of the body it is large enough to play a part in control of the blood concentrations of the major fuels glucose, fatty acids, triacylglycerol and some amino acids. Skeletal muscle contains the largest quantity of protein in the body, which is used as a source of amino acids under various conditions (e.g. starvation, trauma, cancer see above). It plays an important part in the metabolism, in particular, of branched-chain amino acids, glutamine and alanine, which are important in the overall metabolism of amino acids in the body (discussed below). 

In the ebb phase, there is increased activity of the sympathetic nervous system and increased plasma levels of adrenaline and glucocorticoids but a decreased level of insulin. This results in mobilisation of glycogen in the liver and triacylglycerol in adipose tissue, so that the levels of two major fuels in the blood, glucose and long-chain fatty acids, are increased. This is, effectively, the stress response to trauma. These changes continue and are extended into the flow phase as the immune cells are activated and secrete the proinflammatory cytokines that further stimulate the mobilisation of fuel stores (Table 18.2). Thus the sequence is trauma increased endocrine hormone levels increased immune response increased levels of cytokines metabolic responses. 

Figure 5-5. Metabolic activities of major organs during a short-term fast. The importance of the liver in providing glucose to support the brain and other glucose-requiring organs in the post-absorptive state is illustrated. The body relies on available glycogen stores as a ready source for glucose as fuel. PPP, pentose phosphate pathway FA, fatty adds TAG, triacylglycerol.

T Biosynthesis and degradation of triacylglycerols are regulated such that the favored path depends on the metabolic resources and requirements of the moment. The rate of triacylglycerol biosynthesis is profoundly altered by the action of several hormones. Insulin, for example, promotes the conversion of carbohydrate to triacylglycerols (Fig. 21-19). People with severe diabetes mellitus, due to failure of insulin secretion or action, not only are unable to use glucose properly but also fail to synthesize fatty acids from... 

Glucose transport into the adipocyte and its subsequent metabolism are depressed owing to low levels of circulating insulin. This leads to a decrease in fatty acid and triacylglycerol synthesis. 

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