Glucagon
Insulin's counterpart — the hormone that raises blood glucose between meals.
Glucagon is released by the alpha cells of the pancreas when blood glucose falls. It signals the liver to break down stored glycogen and to produce new glucose through gluconeogenesis, holding blood glucose stable during fasting.
It matters because glucose regulation is a two-sided system. Insulin and glucagon oppose each other continuously, and it is their ratio rather than either alone that determines whether the body is storing or mobilising fuel at any moment.
In practice glucagon is also why blood glucose does not crash overnight or during a fast, and it is the active ingredient in the emergency injection used to treat severe hypoglycaemia in people with diabetes.
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Written and reviewed by Mathew Beale, MSc Biotechnology, University of Reading.
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