(the mechanism being that adrenalin pumps into the system, the liver starts burning stored glycogen, turning it into glucose and pumping it into your blood stream - whereas the mechanism of the glucagon shot is the same, but presumably does so as the liver comes into contact with the injected, synthesized
glucagon hormone, as opposed to your pancreas beginning to pump
glucagon into your system once your body's feedback system detects that your overall blood glucose is dropping dramatically.