What does the hormone glucagon do?

Glucagon is an important hormone involved in blood glucose homeostasis. It is released from alpha cells of the pancreas, and helps to increase blood glucose levels, eg. if you have just done lots of exercise, or haven't eaten in a while. Glucagon tells cells of the body to break down glycogen into glucose, and to slow down the rate of respiration so less glucose is metabolised. Both of these actions work to increase the blood glucose concentration.