glucagon
Meaning of glucagon: Insulin takes the attention, but the opposing hormone is what keeps blood sugar from falling too far between meals and overnight.
Definition of glucagon
Glucagon is a hormone made by the alpha cells of the pancreas that raises the amount of sugar circulating in the blood. It is released when blood sugar falls and acts almost entirely on the liver, telling it to release stored sugar and to manufacture more. Insulin does the reverse, and the two together hold blood sugar within a narrow range.
How does it raise blood sugar?
By two routes, both in the liver. The first is fast: the liver keeps a reserve of sugar packed into a storage molecule called glycogen, and glucagon signals it to break that store apart and push glucose back into the blood. The second takes over once the reserve runs down, and involves building fresh glucose out of other materials, chiefly amino acids from protein and the backbone left over from fat. During a long fast glucagon also drives the liver to convert fat into ketones, an alternative fuel the brain can use when sugar is scarce. Muscle keeps its own glycogen but has no receptor for glucagon, so that store stays where it is, reserved for the muscle itself.
How does it sit against insulin?
| Feature | Glucagon | Insulin |
|---|---|---|
| Made by | Alpha cells of the pancreas | Beta cells of the pancreas |
| Released when | Blood sugar falls | Blood sugar rises |
| Effect on the liver | Release and make sugar | Take up and store sugar |
| Net result | Blood sugar rises | Blood sugar falls |
The pairing is why the pancreas is described as holding both halves of a thermostat. What matters to the liver is not either hormone alone but the balance between them, and in diabetes that balance is disturbed on both sides: too little insulin action, and glucagon release that fails to switch off when sugar is already high.
What is it used for as a medicine?
Chiefly as a rescue treatment for severe low blood sugar, where a person is too drowsy or unwell to swallow anything sweet. Injected glucagon pulls sugar out of the liver and buys time, and it depends on that store being present, so it works less well after prolonged starvation or heavy drinking. It has two further uses that have nothing to do with diabetes. It relaxes the muscle of the stomach and intestine, so it is given to still the bowel during certain scans and endoscopies, and it can lift heart rate and contraction in poisoning by drugs that block the heart's usual stimulation.
Used in a sentence
Glucagon was administered to raise the patient's blood sugar during the episode of severe hypoglycemia.
Good to know
Glucagon works by releasing sugar stored in the liver, so its effect depends on that store being present and is reduced when the liver reserve has already been depleted.