Glucagon is a hormone that regulates the body’s blood glucose levels. Its primary purpose is to prevent blood sugar from dropping too low, a condition known as hypoglycemia, by increasing glucose in the bloodstream. This function is part of maintaining a stable energy supply for the body’s cells.
The Pancreas as the Source of Glucagon
Glucagon is produced and secreted by the pancreas, an organ located in the abdomen behind the stomach. The pancreas has an endocrine function, releasing hormones directly into the bloodstream from clusters of cells called the islets of Langerhans.
These islets contain several types of cells, and glucagon is synthesized and released from the alpha cells. When stimulated, these alpha cells release glucagon, which then travels through the blood to its target tissues.
Primary Triggers for Release
The main signal for the pancreas to release glucagon is a decrease in blood glucose levels. When blood sugar falls below a certain threshold, the alpha cells are directly stimulated to secrete the hormone to defend against hypoglycemia.
Other situations can also trigger glucagon release. A meal high in protein can cause a rise in amino acids, which stimulates the alpha cells. This action anticipates the body’s need for glucose to process the protein. Adrenaline, the “fight-or-flight” hormone, can also prompt glucagon secretion during stress or intense exercise to mobilize energy stores.
How Glucagon Raises Blood Sugar
Once in the bloodstream, glucagon travels to its primary target organ: the liver. The liver stores a form of sugar called glycogen and acts as the body’s main glucose reservoir. Glucagon signals the liver to initiate two processes to increase available blood glucose.
The first process is glycogenolysis, where glucagon prompts the liver to break down stored glycogen into glucose molecules. These molecules are then released into the bloodstream, raising blood sugar levels. This is the body’s initial response to low blood sugar.
If glycogen stores are low, glucagon stimulates a second process called gluconeogenesis. This pathway creates new glucose from non-carbohydrate sources, like amino acids and fats. The liver converts these components into glucose, providing a sustained energy source when carbohydrate intake is insufficient.
Glucagon’s Relationship with Insulin
Glucagon operates in a system with another pancreatic hormone, insulin. These two hormones have opposing effects to keep blood sugar levels balanced. While glucagon raises blood sugar, insulin, released from beta cells in the pancreas, lowers it by helping cells absorb glucose from the blood.
This relationship forms a negative feedback loop. When blood sugar is low, glucagon is secreted. As glucagon raises blood sugar, the increase signals the alpha cells to decrease glucagon production.
Conversely, when blood sugar is high after a meal, insulin levels rise and glucagon levels fall. This ensures that glucose is stored and prevents hyperglycemia, or high blood sugar. This communication between alpha and beta cells allows the body to adapt to changing energy demands.