W Interorgan Pathways - Interorgan Metabolic Pathways...

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Interorgan Metabolic Pathways The alanine cycle The Cori cycle Glucose transporters Fuel reserves in organism Starvation and obesity Learning Objectives
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The Cori Cycle High oxygen consumption continuous tens minutes after vigorous muscle activity is over. Lactate produced in the muscle is transported via bloodstream to the liver where it is converted to pyruvate by lactate dehydrogenase. Fig. 22-6
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The Cori Cycle Gluconeogenesis in the liver regenerates glucose from lactate. The process requires ATP, which is produced by the oxidative phosphorylation with consumption of O 2 . If glucose were synthesized by the muscle, the demand of the working muscle for ATP would increase dramatically. During prolonged physical activity, the liver helps muscle to do the job by taking up lactate and returning glucose.
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The Glucose-Alanine Cycle Glycolysis in muscle yields pyruvate that serves as the acceptor of amino group in reactions catalyzed by certain aminotransferases. R-CH(NH 3 + )-COO - + H 3 C-C(O)-COO - R-C(O)-COO - + H 3 C-CH(NH 3 + )-COO - Amino acid Pyruvate -Keto acid Alanine Alanine is released to the bloodstream and transported to the liver. In the liver, alanine is converted to pyruvate, which is used for gluconeogenesis. Fig. 22-7
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The Glucose-Alanine Cycle Glucose produced from pyruvate is returned to muscle. The amino groups transported to the liver with alanine are transformed to urea.
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