Research Notes: Glucose Metabolism

Carbohydrate metabolism begins with digestion in the small intestine where monosaccharides are absorbed into the blood stream. Blood sugar concentrations are controlled by three hormones: insulin, glucagon, and epinephrine. If blood glucose concentration is too high, insulin is secreted by the pancreas and stimulates the transfer of glucose into cells, especially liver and muscle, although other organs are also able to metabolize glucose.

In liver and muscle, most glucose is converted to glycogen by glycogenesis. If blood glucose levels are low, then the hormones epinephrine and glucagon are secreted to stimulate the conversion of glycogen to glucose via glycogenolysis.

If glucose is needed immediately upon entering cells to supply energy, then glycolysis begins, the end products of which are pyruvic acid and ATP. Because glycolysis releases relatively little ATP, further reactions convert pyruvic acid to acetyl CoA and then citric acid in the Kreb's (citric acid) cycle. The majority of ATP is made from oxidative reactions in the Kreb's cycle in connection with the electron transport chain.

During strenuous muscular activity, pyruvic acid is converted into lactic acid rather than acetyl CoA; during rest the lactic acid is converted back to pyruvic acid which in turn is converted back to glucose via gluconeogenesis. If glucose is not needed then, it is converted into glycogen by glycogenesis.

Glucose production is primarily (70-80%) from hepatic glycogenolysis, with 20-25% secondarily from hepatic gluconeogenesis. eMedicine

Resources

• Endotext: Diabetes and Carbohydrate Metabolism

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