Carbohydrate Metabolism

Describe the physiology and biochemistry of fat, carbohydrate and protein metabolism

Storage

Carbohydrates are stored in liver and muscle as glucose polymers known as glycogen.

• The liver contains ~100g of glycogen
  This can maintain plasma glucose for ~24 hours.
• Skeletal muscle contains ~200g of glycogen
  This cannot be released into circulation, and is for use only by the muscle.

Production of glycogen is stimulated by insulin, which is released as plasma glucose levels rise following carbohydrate ingestion. When plasma glucose levels fall, the release of glucagon and adrenaline stimulates glycogenolysis.

Glycolysis

Glycolysis:

• Also known as the Embden-Meyerhof pathway
• Describes the process of converting glucose into pyruvate
• Occurs in the cytoplasm
• Produces 2 ATP
• Does not consume oxygen or produce carbon dioxide Glycolysis can therefore occur under both aerobic and anaerobic conditions.

Gluconeogenesis

Gluconeogenesis is a process that uses ATP to produce glucose from other molecules. Some organs (heart, brain) rely solely on glucose for ATP. Other organs, such as the liver, can generate glucose from:

* Lactate
* Pyruvate
* Glycerol
* Amino acids
* CAC-intermediates

• Simulated by glucagon
• Inhibited by biguanides (metformin)

References

1. Chambers D, Huang C, Matthews G. Basic Physiology for Anaesthetists. Cambridge University Press. 2015.