Glucagon is a hormone produced by the alpha cells within the islets of Langerhans in the pancreas. Its primary role is to regulate blood glucose levels, preventing them from dropping too low. It mobilizes stored glucose during fasting or when dietary intake is insufficient.
Glucagon’s Primary Counterpart: Insulin
Glucagon operates in direct opposition to insulin, forming a “push-pull” system that maintains glucose homeostasis. While insulin works to lower blood sugar by facilitating glucose uptake into cells and promoting its storage as glycogen, glucagon acts to raise blood sugar.
Insulin is released from pancreatic beta cells after meals in response to rising blood glucose levels, signaling the body to store excess glucose. Glucagon, conversely, is released by alpha cells when blood glucose levels fall during fasting or between meals. This dynamic balance ensures cells receive adequate energy and prevents the harmful effects of prolonged high or low blood sugar.
How Glucagon Raises Blood Sugar
Glucagon interacts primarily with the liver to increase blood glucose concentrations. When blood sugar is low, glucagon stimulates glycogenolysis, the breakdown of stored glucose into individual glucose molecules. These glucose molecules are then released into the bloodstream, raising blood sugar levels.
As glycogen stores become depleted, especially during prolonged fasting, glucagon promotes gluconeogenesis. This process involves the creation of new glucose from non-carbohydrate sources, such as amino acids, lactate, and glycerol. While the liver is the primary site for gluconeogenesis, the kidneys also contribute to this process. Glucagon also reduces the liver’s uptake and storage of glucose, ensuring more glucose remains in circulation.
Interactions with Other Hormones and Nutrients
Beyond its direct interaction with glucose and insulin, glucagon’s release and actions are influenced by other substances. For example, certain amino acids, particularly after a protein-rich meal, can stimulate glucagon secretion. This ensures that even when carbohydrate intake is low, the body can still mobilize glucose from other sources.
Stress hormones like epinephrine (adrenaline) and cortisol also interact with glucagon to elevate blood glucose. Epinephrine can enhance glucagon’s effects on glucose production and interfere with glucose uptake by cells, contributing to hyperglycemia during stress. Cortisol can further sustain these elevations in glucose production, amplifying the impact of glucagon and epinephrine on blood sugar levels. These synergistic interactions highlight how multiple hormonal systems coordinate to manage the body’s energy resources.
Glucagon Interactions in Health and Disease
The intricate interactions of glucagon can become dysregulated in various health conditions, particularly diabetes. In Type 2 diabetes, glucagon levels can be inappropriately high, contributing to persistently elevated blood glucose (hyperglycemia). This excess glucagon stimulates the liver to produce more glucose, exacerbating the high blood sugar characteristic of the condition.
In Type 1 diabetes, the glucagon response to low blood sugar can be impaired, making individuals more susceptible to severe hypoglycemia. Glucagon injections are also a therapeutic intervention for severe hypoglycemia, providing a rapid increase in blood sugar by stimulating the liver to release stored glucose. Glucagon-secreting tumors, known as glucagonomas, are rare but can cause excessive glucagon production, leading to severe hyperglycemia, weight loss, and a distinctive skin rash called necrolytic migratory erythema. These examples show the broad impact of glucagon’s interactions on overall health and disease management.