The action of the hormone glucagon works in the opposite direction to insulin. Glucagon causes the blood glucose level to rise if it has fallen too low. It does this by stimulating the liver, muscles and body fat to release their stored glucose back into the blood.
You may wonder why the body needs a hormone to increase glucose levels. Besides regulating the blood glucose level so that it does not rise too high, the body also needs to be protected from glucose levels that are too low. The brain does not function properly if glucose levels in the blood drop even a small amount below normal, and if they drop further still the person becomes confused and eventually becomes unconscious. Brain damage and eventually death results if the brain is starved of glucose for a long period.