Insulin and Glucagon

What is the overall role of insulin?

Insulin signals a "fed state" and promotes storage of fuel and use of glucose.

What is the overall role of glucagon?

Glucagon signals a "fasting state" and promotes release of stored fuels and production of glucose.

Which organ does insulin heavily target?

Liver

Which organ does glucagon primarily target?

Mainly the liver (muscle lacks glucagon receptors).

INSULIN effect on the liver

Stimulates glycogen synthesis; increases glycolysis; increases fatty acid synthesis; decreases gluconeogenesis; promotes storage.

GLUCAGON effect on the liver

Stimulates glycogen breakdown; increases gluconeogenesis; increases fatty acid oxidation; produces glucose for the blood.

INSULIN effect on muscle

Promotes GLUT4 insertion → increased glucose uptake; increases glycogen synthesis; increases protein synthesis.

GLUCAGON effect on muscle

No direct effect (muscle lacks glucagon receptors).

INSULIN effect on adipose tissue

Increases glucose uptake via GLUT4; increases triglyceride synthesis; inhibits lipolysis.

GLUCAGON effect on adipose tissue

Stimulates lipolysis → releases fatty acids for energy.

INSULIN effect on blood glucose levels

Decreases blood glucose.

GLUCAGON effect on blood glucose levels

Increases blood glucose.

INSULIN effect on glycolysis

Glycolysis increases (uses glucose for energy/storage).

GLUCAGON effect on glycolysis

Glycolysis decreases in the liver.

INSULIN effect on gluconeogenesis

Insulin inhibits gluconeogenesis.

GLUCAGON effect on gluconeogenesis

Glucagon strongly activates gluconeogenesis.

How does insulin affect fatty acid metabolism?

Increases fatty acid synthesis in liver; increases triglyceride storage in adipose.

How does glucagon affect fatty acid metabolism?

Stimulates breakdown of fats (lipolysis) and fatty acid oxidation.

Which transporter does insulin activate?

GLUT4 (muscle + adipose).

Which transporter does glucagon activate?

None; glucagon does not directly regulate glucose transport.

How do beta cells sense glucose?

Via GLUT2 import → glucose → G6P → ATP production → insulin release.

How do alpha cells respond to low glucose?

Low glucose → increased glucagon secretion.

Insulin state summary

"Fed state: store fuel

Glucagon state summary

"Fasting state: release fuel