Carbohydrate gluconeogenesis

Just as fatty acids are catabolized and anabolized by different pathways, so too are carbohydrates. Gluconeogenesis, the anabolic pathway by which organisms make glucose from pyruvate, is related to glycolysis but is not its exact reverse. The gluconeogenesis pathway is shown in Figure 29.9 (p. 1222). 

The most important gluco-C. hormone is hydrocortisone which is excreted by the adrenal cortex into the blood as response to physical and psychic stress (the normal average rate of formation in humans amounts to about 20 mg/d for comparison corticosterone ca. 3 mg and aldosterone 0.3 mg). Hydrocortisone promotes the conversion of proteins and lactate into energy-rich carbohydrates (gluconeogenesis), storage of the latter as glycogen, and stimulates the formation of storage (depot) fats (lipids). In addition, hydrocortisone prevents or reduces tissue reactions to inflam-... 

Biomolecules are synthesized as well as degraded, but the pathways for anabolism and catabolism are not the exact reverse of one another. Fatty acids are biosynthesized from acetate by an 8-step pathway, and carbohydrates are made from pyruvate by the 11-step gluconeogenesis pathway. 

The citric acid cycle is the final common pathway for the aerobic oxidation of carbohydrate, lipid, and protein because glucose, fatty acids, and most amino acids are metabolized to acetyl-CoA or intermediates of the cycle. It also has a central role in gluconeogenesis, lipogenesis, and interconversion of amino acids. Many of these processes occur in most tissues, but the hver is the only tissue in which all occur to a significant extent. The repercussions are therefore profound when, for example, large numbers of hepatic cells are damaged as in acute hepatitis or replaced by connective tissue (as in cirrhosis). Very few, if any, genetic abnormalities of citric acid cycle enzymes have been reported such ab-normahties would be incompatible with life or normal development. 

Gluconeogenesis is the process of converting noncarbohydrates to glucose or glycogen. It is of particular importance when carbohydrate is not available from the diet. Significant substrates are amino acids, lactate, glycerol, and propionate. 

Gluconeogenesis Formation of glucose from precursors other than carbohydrates (especially by the liver and kidney) using amino acids from proteins, glycerol from fats, or lactate produced by muscle during anaerobic glycolysis. 

Carbohydrate Metabolism Glycolysis/ Gluconeogenesis Citrate cycle (TCA cycle)... 

The liver not only extracts glucose from the blood in the postprandial state and stores it as glycogen, but is also able to synthesize glucose from non-carbohydrate sources via gluconeogenesis, therefore the liver is crucial in regulating glucose homeostasis. 

Gluconeogenesis glucose formation from non-carbohydrate sources... 

GLUCONEOGENESIS GLUCOSE FORMATION FROM NON-CARBOHYDRATE SOURCES... 

Gluconeogenesis is the de novo synthesis of glucose from none carbohydrate sources. These sources (precursors) are lactic acid, glycerol and the amino acids, especially alanine, glntamine and aspartic acid (Fignre 6.22). 

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