gluconeogenees

Gluconeogenesis is a metabolic pathway that results in the generation of glucose from certain non-carbohydrate carbon substrates. This process occurs primarily in the liver and kidney cortex, serving as a crucial mechanism for maintaining blood glucose levels, especially during periods of fasting or prolonged exercise when carbohydrate intake is insufficient. The substrates for gluconeogenesis can include amino acids (from protein breakdown), lactate (from anaerobic glycolysis), and glycerol (from triglyceride breakdown).

The pathway essentially reverses many steps of glycolysis, but it requires several bypass reactions to overcome thermodynamically unfavorable steps. Key enzymes involved include pyruvate carboxylase, phosphoenolpyruvate carboxykinase, fructose-1,6-bisphosphatase, and glucose-6-phosphatase. These enzymes facilitate the conversion of pyruvate (a product of lactate or amino acid metabolism) into glucose-6-phosphate, which can then be dephosphorylated to free glucose.

Gluconeogenesis is tightly regulated by hormonal signals, primarily insulin and glucagon. Glucagon promotes gluconeogenesis when blood glucose is low, while insulin inhibits it when blood glucose levels are high. This interplay ensures that the body has a continuous supply of glucose for energy, particularly for tissues like the brain and red blood cells that rely heavily on glucose. While essential for survival, excessive gluconeogenesis can contribute to hyperglycemia in certain conditions.