Describe the changes that take place to maintain glucose concentration in exercise.

During exercise, blood glucose concentration falls due to the increased energy demand and glucose uptake of skeletal muscles. This fall in glucose concentration is detected by the alpha and beta cells in the Islets of Langerhans of the pancreas, resulting in decreased insulin release from the beta cells and increased glucagon release from the alpha cells into the bloodstream. Once released, glucagon binds to receptors on hepatocytes (liver cells) and induces gluconeogensis (literally, the "creation of new glucose"). Gluconeogenesis is the process of converting glycogen to glucose, which is then released into the blood stream and raises blood glucose concentrations to healthy levels. This process is a good example of negative feedback, where the stimulus (blood concentration) is detected (in the pancreas' Islets of Langerhans) and compared to a set point. If the stimulus is different to the desired level, changes will be made to bring the stimulus closer to the set point. In the case of glucose control, insulin and glucagon are used to adjust glucose concentrations. This system famously breaks down in diabetes, where glucose levels are poorly regulated and dangerously high.