Glucagon: what kind of hormone is it and what does it do

Almost everyone has heard of insulin, but glucagon is noticeably less well known. It is the second hormone of the pancreas, which works in tandem with insulin and is linked to blood sugar levels. Let's break down what it does and why it matters.

What glucagon is

Glucagon is a peptide hormone of the alpha cells of the islets of Langerhans in the pancreas. Its molecule consists of 29 amino acids, molecular weight — 3485 daltons. The hormone was discovered in 1923 by Kimball and Murlin. In the simplest terms, it is a chemical signal "glucose is needed right now": it raises blood sugar when it drops.

Where glucagon is produced

Glucagon is produced by the alpha cells of the islets of Langerhans in the pancreas, next to the beta cells that make insulin. The hormone then enters the blood and finds its target in the liver, where there are specific glucagon receptors. But in skeletal muscle there are practically no such receptors, so the hormone has almost no effect on muscle glycogen.

How glucagon affects blood glucose levels

The mechanics are as follows: the hormone binds to a receptor on the liver cell membrane, activates adenylate cyclase, cAMP levels rise — and then a cascade of reactions follows. In the liver this activates glycogen phosphorylase and inhibits glycogen synthase, glycogen breaks down to glucose-1-phosphate, which is converted to glucose-6-phosphate, and from it free glucose is formed, which enters the blood. This is how sugar is kept at a constant level.

• breakdown of glycogen in the liver (glycogenolysis);
• synthesis of glucose from other substances (gluconeogenesis);
• activation of lipolysis — the breakdown of fats;
• activation of ketogenesis — the formation of ketone bodies;
• enhanced secretion of insulin by healthy beta cells.

The last point looks strange, but it is a physiological brake: glucagon itself raises sugar and itself triggers the counteracting mechanism. The hormone also affects the heart — it raises blood pressure, heart rate and contraction force — and participates in "fight or flight" reactions, increases the secretion of catecholamines by the adrenal medulla.

Glucagon and insulin: how they differ and how they interact

Insulin lowers glucose, glucagon raises it. When blood sugar rises, the pancreas releases insulin, and glucose enters the cells for energy. When it falls, glucagon takes over and pulls glucose out of the liver depot. The result is a seesaw that is almost unnoticeable in a healthy person. In a person with diabetes, insulin is insufficient or works worse than it should: glucose remains in the blood and does not reach the cells.

Glucagon in diabetes and hypoglycemia

Hypoglycemia is a low glucose level. For people with diabetes this is usually below 70 milligrams per deciliter, for people without diabetes — below 55 milligrams per deciliter. Most often it occurs in people with type 1 diabetes or with type 2 diabetes who receive insulin or other glucose-affecting drugs.

Symptoms appear quickly: hunger, dizziness, anxiety or irritability, sweating, trembling, tingling of the lips, palpitations, fatigue, vision changes such as blurriness, confusion. In severe hypoglycemia, seizures and loss of consciousness are possible. This is where glucagon comes in as a medicine: it raises glucose levels and is available as a nasal spray or injection. People with diabetes may be prescribed such a kit by a doctor for an emergency situation. There is also a blood test for glucagon.

When to see a doctor

You should see a doctor if a person with diabetes has frequent hypoglycemia, has had severe or nighttime episodes, and also if the symptoms of low sugar are no longer recognized. If there is no diabetes but there is trembling, sweating, rapid heartbeat and confusion — that is also a reason to investigate. In people without diabetes the causes vary: liver and kidney disease, hormone deficiency, weight-loss surgery, certain medications, malnutrition, Addison's disease, a pancreatic tumor. Which tests are needed is decided by the doctor.

Hypoglycemia by itself is not a reason to call an ambulance. Call 103 or 112 — if a person with very low sugar is not responding normally or is unconscious, and there is no glucagon or no one knows how to use it, if they have not come round within 10 minutes after glucagon administration, or if they had been drinking alcohol beforehand.

This material is for reference: it explains how the hormone works but does not replace a doctor's consultation — figures and decisions about testing are best discussed with a doctor.

This content is for reference and does not replace a doctor's consultation. Medical disclaimer