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How do insulin and glucagon control blood glucose levels?

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Insulin and glucagon are hormones produced by the islets of Langerhans in the pancreas that work in opposition to maintain blood glucose homeostasis.123

Insulin: The Fed State

When blood glucose levels rise after a meal, beta cells secrete insulin. Insulin lowers blood glucose by:23
* Promoting the uptake of glucose into liver, muscle, and adipose tissue.23
* Encouraging the storage of glucose as glycogen (glycogenesis) and inhibiting its breakdown.23
* Decreasing gluconeogenesis, the production of glucose from non-carbohydrate sources.23

Glucagon: The Fasting State

When blood glucose levels drop, alpha cells secrete glucagon to raise glucose concentrations. Glucagon acts primarily on the liver to:13
* Stimulate glycogenolysis, the breakdown of stored glycogen into glucose.14
* Promote gluconeogenesis to produce new glucose from amino acids and glycerol.13

Together, these hormones ensure that blood sugar remains within a narrow, healthy range, providing a constant energy supply for the body and brain.34