Carbohydrate metabolism

Most important ones: glucose, galactose, and fructose

3 parts of carbohydrate metabolism

1. Glycolysis
   (aka Embden-Meyerhof pathway)
2. Citric acid cycle
   (aka Krebs cycle)
3. Oxidative phophorylation

Other pathways in carbohydrate metabolism

• Glycogenesis
• Direct oxidative pathway
  (aka hexose monophosphate shunt)
  (aka pentose phosphate pathway)
• 2,3 bisphophoglycerate
  (aka 2,3-diphosphoglycerate, 2,3-DPG)

Other notes on carbohydrate metabolism

Fructose

Fructose is converted to:

• fructose 6-phosphate by hexokinase, OR, 
• fructose 1-phosphate by fructokinase
  * Majority
  * Independent of insulin

Fructose 6-phosphate can then be converted to:

• fructose 1,6-phosphate, OR,
• fructose 2,6-phosphate

Fructose 2,6-phosphate

[WG21:p295]

Potent regulator of hepatic gluconeogenesis

When level of F2,6P is high
-> Conversion of F6P to F1,6P increased
-> Increased glycolysis

When level of F2,6P is low
-> Conversion of F1,6P to F6P increased
-> Increased gluconeogenesis

Catecholamine

• Liver
  * beta-receptor --> increase cAMP
  * alpha-receptor --> increase intracellular [Ca2+]
  * Both increase gluconeogenesis
  --> Increase hepatic glucose output
• Muscle
  * Same mechanism
  * Absence of glucose 6-phosphatase
  --> Lactate released from muscles
  --> Converted to glycogen in liver
  --> Increase hepatic glycogen content
• NE and E both increase FFA release into circulation
• E decrease peripheral utilization of glucose