What role does glucagon play in glucose homeostasis?

Glucagon primarily functions to increase blood glucose levels, which is crucial for maintaining glucose homeostasis, particularly during periods of fasting or when blood sugar levels drop. This hormone is secreted by the alpha cells of the pancreas and acts on the liver to promote gluconeogenesis, the process of generating glucose from non-carbohydrate sources, and glycogenolysis, the breakdown of glycogen into glucose.

When blood glucose levels are low, glucagon is released into the bloodstream, binding to receptors on liver cells and stimulating these processes. As a result, more glucose is released into the bloodstream, raising blood glucose levels and ensuring that the body has a sufficient energy supply, especially for vital organs like the brain that rely heavily on glucose. This action is an essential counter-regulatory mechanism to insulin, which lowers blood glucose levels, thus highlighting glucagon's vital role in glucose regulation and homeostasis.