Glucagon, a peptide hormone secreted by the pancreas, raises blood glucose levels. Its effect is opposite that of insulin, which lowers blood glucose levels. The pancreas releases glucagon when blood sugar (glucose) levels fall too low. Glucagon causes the liver to convert stored glycogen into glucose, which is released into the bloodstream. High blood glucose levels stimulate the release of insulin. Insulin allows glucose to be taken up and used by insulin-dependent tissues. Thus, glucagon and insulin are part of a feedback system that keeps blood glucose levels at a stable level. Glucagon belongs to a family of several other related hormones.
Secretion of glucagon is stimulated by:
- Hypoglycemia
- Epinephrine (via β2, α2, and α1 adrenergic receptors)
- Arginine
- Alanine (often from muscle-derived pyruvate/glutamate transamination (see alanine transaminase reaction).
- Acetylcholine
- Cholecystokinin
Secretion of glucagon is inhibited by:
- Somatostatin
- Insulin (via GABA)
- Increased free fatty acids and keto acids into the blood
- Increased urea production
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