What is the primary action of glucagon on hepatic metabolism during fasting?

• A. Stimulates glycolysis and glycogen storage
• B. Stimulates gluconeogenesis and glycogenolysis, increases ketogenesis, raises blood glucose
• C. Inhibits ketogenesis
• D. Inhibits hepatic glucose production

Answer: (B)

Glucagon’s main action during fasting is to make the liver release glucose into the blood. It binds to liver receptors and raises cAMP, activating pathways that push glucose production. The liver does two things: it breaks down stored glycogen (glycogenolysis) and it makes new glucose from non-carbohydrate sources (gluconeogenesis). At the same time, low insulin means fat is mobilized and fatty acids flow to the liver, where they fuel ketone production (ketogenesis) to supply other tissues with energy. Together, these actions raise blood glucose and provide alternative fuel during fasting.

Other options describe effects that don’t fit glucagon’s fasting role: it does not promote glycolysis or glycogen storage, and it does not inhibit ketogenesis or hepatic glucose production.