Gluconeogenesis

Gluconeogenesis refers to the process of making glucose from noncarbohydrate substances. Blood glucose is critical for central nervous system function, aids in the metabolism of fat, and supplies fuel to working cells. However, because of its limited storage capacity, a minimum level of glucose is always available through the manufacture of glucose from noncarbohydrate substances. There are three systems for gluconeogenesis:

1. Triglycerides are the predominant storage form of fat in the human body and consist of three fatty acids attached to a glycerol molecule. The breakdown of triglycerides results in free glycerol molecules (a three-carbon substance), and the combination of two glycerol molecules in the liver results in the production of one glucose molecule (a six-carbon substance).
2. Catabolized muscle protein results in an array of free amino acids that constituted the building blocks of the muscle. One of these amino acids, alanine, can be converted by the liver to form glucose.
3. In anaerobic glycolysis, lactic acid is produced. This lactic acid, or lactate, can be converted back to pyruvic acid for the aerobic production of ATP, or two lactic acid molecules can combine in the liver to form glucose. The conversion of lactate to glucose is referred to as the Cori cycle (lactate removed from the muscle and glucose returned to the muscle). If blood glucose is low, pyruvic acid can be converted to lactate, and glucose can be produced via the Cori cycle.