Glucagon

• It raises blood glucose by stimulating the conversion of glycogen into glucose in the liver only (muscle glycogen cannot give glucose to the blood).
• It is antagonistic to insulin.

Negative feedback:

• After a meal, blood glucose rises → β cells release insulin → glucose enters cells and is stored → blood glucose falls to normal.
• During fasting or exercise, blood glucose falls → α cells release glucagon → liver glycogen is converted to glucose → blood glucose rises.