Final answer:
During fasting, cortisol contributes to raising blood glucose levels by stimulating the breakdown of muscle proteins and reducing the muscle's uptake of glucose.
Step-by-step explanation:
During fasting, cortisol increases blood glucose levels by stimulating protein catabolism and reducing glucose uptake in muscle. This process involves the breakdown of muscle proteins to amino acids, which are then released into the bloodstream and taken up by the liver. The liver converts these amino acids into glucose via gluconeogenesis, contributing to the maintenance of blood glucose levels during periods of low intake.