Name a key metabolic pathway through which glucagon acts to increase glucose levels.

Glucagon primarily acts to increase glucose levels through the process of glycogenolysis. This metabolic pathway involves the breakdown of glycogen, a stored form of glucose found in the liver and muscle cells, into glucose molecules that can be released into the bloodstream. When blood glucose levels are low, glucagon is secreted by the alpha cells of the pancreas, signaling the liver to convert glycogen back into glucose. This glucose is then made available for use by the body's tissues, particularly during periods of fasting or intense physical activity.

In contrast, glycolysis is a pathway that breaks down glucose for energy rather than increasing glucose levels, while fatty acid synthesis involves creating fat from carbohydrates and does not contribute to raising blood glucose. Protein metabolism typically refers to the breakdown and utilization of proteins for energy or other functions, which also does not have a direct role in increasing glucose levels like glycogenolysis does. Therefore, glycogenolysis is a critical pathway for glucagon’s action in maintaining proper glucose homeostasis in the body.