How the body produces glucose when we are fasting
Glucose is our main source of energy and it is therefore important that there are physiological pathways in place to prevent blood glucose from dropping dangerously low when we are fasting, for example when sleeping at night.
Gluconeogenesis: producing glucose from non-carbohydrate sources
The gluconeogenesis pathway (see metabolism figure below) synthesises new glucose using non-carbohydrate precursors (glycerol from the breakdown of triglycerides, lactate during anaerobic glycolysis and amino acids from muscle protein degradation). 90% of gluconeogenesis occurs in the liver but some occurs in the kidney too. Insulin regulates gluconeogenesis. The newly made glucose is released back into the blood stream to raise blood glucose levels.
Figure: gluconeogenesis and glycogenesis pathways in the metabolism
Glycogenolysis: release of glucose from stored glycogen
In the glycogenolysis pathway (see metabolism figure above), liver glycogen can be broken down to produce glucose which is released back into the blood stream to increase blood glucose concentrations. The combination of these processes enables us to maintain a low but significant level of glucose, despite fasting or even starvation (see figure below). Figure: release of glucose from stored glycogen
So you can see from the diagram above that the blood glucose (black line) is kept constant by a combination of processes: release of glucose from the diet (red line), gluconeogenesis (blue) and glycogenolysis (green).
© University of Southampton 2017