How does glucagon affect blood glucose levels?

Glucagon is a hormone produced by the alpha cells of the pancreas, and its primary role is to increase blood glucose levels, especially during times of fasting or low blood glucose. It achieves this primarily through two key mechanisms: glycogenolysis and gluconeogenesis.

Glycogenolysis is the process by which glycogen, a stored form of glucose in the liver and muscles, is broken down into glucose molecules. When glucagon is released, it stimulates the liver to convert glycogen into glucose, which is then released into the bloodstream, thereby raising blood glucose levels.

Gluconeogenesis is another process stimulated by glucagon, where the liver generates glucose from non-carbohydrate sources, such as amino acids or glycerol. This process is particularly important during prolonged periods of fasting when glycogen stores are depleted, allowing the body to maintain adequate blood glucose levels.

Overall, by stimulating both glycogenolysis and gluconeogenesis, glucagon effectively increases the availability of glucose in the bloodstream, providing energy for the body's needs, especially for critical functions like maintaining brain function. This highlights why the correct answer accurately reflects glucagon's role in raising blood glucose levels.