The roles of glucagon and insulin.
Glucagon is a hormone secreted by the islets of Langerhans in the pancreas, which increases the concentration of glucose in the blood by stimulating the metabolic breakdown of glycogen. It is thus antagonistic to (i.e., counteracts the effects of) insulin (see antagonist).
Glucagon is a 29 amino acid polypeptide.
It is administered by injection to counteract diabetic hypoglycemia.