Glükkoneogenees

Glükkoneogenees 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, to a lesser extent, in the kidney cortex. It is essential for maintaining blood glucose levels, especially during periods of fasting, starvation, or intense exercise when glucose intake from the diet is insufficient. The body's reliance on glucose as a primary energy source for the brain and red blood cells necessitates this continuous production.

The substrates for gluconeogenesis include pyruvate, lactate, glycerol, and glucogenic amino acids. Pyruvate can be derived from lactate produced during anaerobic glycolysis (the Cori cycle) or from the breakdown of amino acids. Glycerol is released from the hydrolysis of triglycerides in adipose tissue. Glucogenic amino acids are those that can be catabolized to intermediates of the citric acid cycle or to pyruvate, which can then be converted to glucose.

Gluconeogenesis is not simply the reverse of glycolysis, although many of the enzymes are shared. Three key irreversible steps in glycolysis are bypassed by specific enzymes in gluconeogenesis. These include the conversion of pyruvate to phosphoenolpyruvate, fructose-1,6-bisphosphate to fructose-6-phosphate, and glucose-6-phosphate to glucose. Hormonal regulation plays a crucial role, with glucagon and cortisol promoting gluconeogenesis, while insulin inhibits it. This hormonal control ensures that glucose is produced when needed and conserved when blood glucose levels are high.