Glucagon is a hormone that maintains the body’s glucose balance, acting as a counter-balance to insulin. When blood sugar levels drop below a healthy range, specialized alpha cells within the pancreas release glucagon into the bloodstream. The hormone’s primary function is to signal the liver to release its stored glucose, raising blood sugar and preventing hypoglycemia. This release is part of the body’s automatic defense system to ensure the brain and other organs receive a steady supply of fuel.
How Glucagon Signals the Liver to Produce Glucose
The liver is the central target organ for glucagon, containing specific receptors that bind to the hormone and initiate metabolic events. Once glucagon attaches to a liver cell receptor, it activates an internal signaling cascade involving cyclic AMP (cAMP). This cascade redirects the liver cell’s metabolic machinery toward glucose production.
Glycogenolysis
The first process triggered is glycogenolysis, the rapid breakdown of glycogen, which is the stored form of glucose in the liver. Glucagon activates enzymes, such as glycogen phosphorylase, that quickly clip individual glucose molecules from these large chains. The freed glucose is then released directly into the bloodstream, providing a fast source of sugar.
Gluconeogenesis
The second, more sustained process is gluconeogenesis, which is the creation of new glucose. This pathway uses non-carbohydrate sources, such as amino acids from muscle protein and glycerol from fat breakdown, as building blocks. Gluconeogenesis is important during prolonged fasting or when the liver’s glycogen stores have been depleted. Both processes work together to ensure an increasing flow of glucose into the circulation.
Variables That Influence Glucagon’s Effectiveness
The blood sugar rise produced by glucagon depends on several biological factors. The most important factor is the current level of glycogen stores held within the liver. If a person has been fasting or has low liver glycogen, the glucagon-induced breakdown of stored sugar will be significantly limited.
The overall health and function of the liver also modify the response, as this organ is solely responsible for processing glucose. Liver impairment can reduce the organ’s capacity to respond fully to the hormone. Furthermore, the presence of insulin directly affects glucagon’s action. High circulating insulin can counteract the glucose-raising effect of glucagon, as insulin promotes glucose uptake and storage.
Measuring the Typical Blood Sugar Increase
In a clinical setting, a standard dose of injected glucagon is used for the emergency treatment of severe hypoglycemia. Following a 1-milligram injection, blood glucose levels typically begin to rise within 10 minutes. The maximum concentration of glucose in the blood is usually observed about 30 minutes after administration.
After a 1-milligram dose, blood glucose levels can rise significantly, often peaking around 136 to 138 milligrams per deciliter (mg/dL) in non-hypoglycemic volunteers. For individuals experiencing severe low blood sugar, the goal is to safely restore blood sugar above the threshold of approximately 70 mg/dL. The hyperglycemic effect generally lasts for 60 to 90 minutes, providing a temporary window for the person to consume carbohydrates and stabilize glucose levels.
Emergency Use of Glucagon in Hypoglycemia
Glucagon is commonly used in the emergency treatment of severe hypoglycemia, especially for individuals with diabetes who use insulin. The standard emergency dose for adults and children over 25 kilograms is 1 milligram, delivered via intramuscular or subcutaneous injection. A 3-milligram dose of nasal powder is also available.
The rapid action of glucagon often restores consciousness within 15 minutes of administration. If the person does not awaken within this timeframe, a second dose may be administered while waiting for emergency medical services. Once the person is awake and able to swallow safely, follow the administration with fast-acting carbohydrates. This follow-up step is crucial for replenishing the liver’s depleted glycogen stores and preventing a second episode of low blood sugar.