How does glucagon work?
“When blood sugar levels are too low, the pancreas releases glucagon into the bloodstream. This hormone acts as an antagonist to insulin. It causes the liver cells of the liver to release stored sugar and to convert proteins into sugar to make them available as a source of energy too. The flow of glucagon is stopped once blood sugar levels rise.” https://www.ncbi.nlm.nih.gov/pubmedhealth/PMH0072490/
http://www.hormone.org/hormones-and-health/hormones/glucagon