Gluconeogenesis is the term used to include all pathways responsible for converting all non-carbohydrate precursors to glucose or glycogen. Liver and kidney are the major gluconeogenic tissues. Gluconeogenesis meets the glucose requirement of the body when carbohydrate is not available in the required amount from the diet or from glycogen reserves. Erythrocytes and nervous systems especially require glucose as energy fuel, so supply of glucose is a must for these tissues. Failure of gluconeogenesis is usually fatal. Failure of gluconeogenesis is usually fatal.