Blood sugar levels are an important part of overall health. When blood sugar levels drop, an individual may feel lethargic. If they drop too low, the individual may become disoriented, dizzy or even pass out. Blood sugar control involves a complex system of hormones, and one of those hormones is glucagon.
What is glucagon?
Glucagon is a hormone that is produced by alpha cells in a part of the pancreas known as the islets of Langerhans. It is a hormone that is involved in controlling blood sugar (glucose) levels so in contrast to the glucose-depositing nature of insulin action, glucagon acts as a glucose-mobilizing hormone.
What does glucagon do?
Glucagon works to counterbalance the actions of insulin.
Glucagon works with your liver to turn a type of stored sugar called glycogen into glucose. Glucose goes from your liver into your blood to give you energy.
Glucagon can tell your liver not to take in too much glucose from the food you eat and to release stored sugar into your blood instead. This can keep your glucose levels steady.
About four to six hours after you eat, the glucose levels in your blood decrease, triggering your pancreas to produce glucagon. This hormone signals your liver and muscle cells to change the stored glycogen back into glucose. These cells then release the glucose into your bloodstream so your other cells can use it for energy.
This whole feedback loop with insulin and glucagon is constantly in motion. It keeps your blood sugar levels from dipping too low, ensuring that your body has a steady supply of energy.
Glucagon’s role in the body is to prevent blood glucose levels dropping too low. To do this, it acts on the liver in several ways:
- It stimulates the conversion of stored glycogen (stored in the liver) to glucose, which can be released into the bloodstream. This process is called glycogenolysis.
- It promotes the production of glucose from amino acid molecules. This process is called gluconeogenesis.
- It reduces glucose consumption by the liver so that as much glucose as possible can be secreted into the bloodstream to maintain blood glucose levels.
Glucagon also acts on adipose tissue to stimulate the breakdown of fat stores into the bloodstream.
Glucagon Increases Hepatic Glucose Production
Glucagon controls plasma glucose concentrations during fasting, exercise and hypoglycemia by increasing hepatic glucose output to the circulation. Specifically, glucagon promotes hepatic conversion of glycogen to glucose.
Glucagon Stimulates Break-Down of Fatty Acids and Inhibits Lipogenesis in the Liver
Glucagon promotes formation of non-carbohydrate energy sources in the form of lipids and ketone bodies. Thereby, glucagon contributes to a stable energy homeostasis during conditions where energy supply is limited (fasting) or in states of increased energy demand.
Glucagon Promotes Break-Down of Amino Acids
During prolonged fasting, glucagon stimulates formation of glucose from amino acids (via gluconeogenesis) by upregulating enzymes involved in the process. However, the rate-limiting step of the process depends on the supply of gluconeogenic amino acids from muscle or dietary intake, a process not controlled by glucagon.
Glucagon Reduces Food Intake
Acute administration of glucagon has been shown to reduce food intake and diminish hunger. The mechanism behind glucagon’s potential appetite-reducing effect is not fully understood but could arise from hepatic metabolic changes induced by glucagon or from glucagon working directly in the central nervous system.
Glucagon Increases Energy Expenditure
In addition to a potential effect of glucagon on food intake, evidence suggests that glucagon contributes to a negative energy balance by stimulating energy expenditure. In humans, this effect has been observed in studies in which glucagon infusion resulted in increases in resting energy expenditure.
Glucagon May Regulate Heart Rate and Contractility
Infusion of high doses of glucagon increases heart rate and cardiac contractility. In comparison, glucagon concentrations within the normal physiological range do not appear to affect heart rate or contractility and any physiological role of endogenous glucagon in the regulation of pulse rate remains questionable.
How is glucagon controlled?
Glucagon works along with the hormone insulin to control blood sugar levels and keep them within set levels. Glucagon is released to stop blood sugar levels dropping too low (hypoglycaemia), while insulin is released to stop blood sugar levels rising too high (hyperglycaemia).
The release of glucagon is stimulated by low blood glucose, protein-rich meals and adrenaline (another important hormone for combating low glucose). The release of glucagon is prevented by raised blood glucose and carbohydrate in meals, detected by cells in the pancreas.
In the longer-term, glucagon is crucial to the body’s response to lack of food. For example, it encourages the use of stored fat for energy in order to preserve the limited supply of glucose.
What happens if I have too much glucagon?
A rare tumour of the pancreas called a glucagonoma can secrete excessive quantities of glucagon. This can cause diabetes mellitus, weight loss, thrombosis, venous thrombosis and a characteristic skin rash.
What happens if I have too little glucagon?
Unusual cases of deficiency of glucagon secretion have been reported in babies. This results in severely low blood glucose which cannot be controlled without administering glucagon.
Glucagon can be given by injection to restore blood glucose lowered by insulin (even in unconscious patients). It can increase glucose release from glycogen stores more than insulin can suppress it. The effect of glucagon is limited, so it is very important to eat a carbohydrate meal once the person has recovered enough to eat safely.
Glucagon in diabetes
In people with diabetes, glucagon’s presence can raise blood glucose levels too high.
The reason for this is either because not enough insulin is present or, as is the case in type 2 diabetes, the body is less able to respond to insulin.
In type 1 diabetes, high levels of circulating insulin can inhibit the release of glucagon in response to hypoglycemia.