Insulin is released in response to elevated blood glucose levels during the fed state. It promotes glucose uptake by cells, glycogenesis, and lipogenesis while inhibiting gluconeogenesis and glycogenolysis.
Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate precursors (e.g., amino acids, lactate) in the liver during fasting when glycogen stores are exhausted.
During prolonged starvation, ketogenesis occurs in the liver, producing ketone bodies (e.g., acetoacetate, β-hydroxybutyrate) as an alternative energy source for the brain and other tissues.
The Cori cycle involves lactate produced by anaerobic glycolysis in muscles being transported to the liver, where it is converted back to glucose through gluconeogenesis. This glucose is then returned to the muscles for energy.
During intense physical activity, the demand for ATP is immediate, and glycolysis (anaerobic metabolism) becomes the primary source of ATP because it is faster than oxidative phosphorylation, though less efficient.
