Glucagon is an endocrine hormone that helps to control blood sugar levels. Glugacon is the "opposite" of the better known [insulin]. While insulin reduces the level of glucose in the blood glucagon increases it. Both glucagon and insulin are secreted in the [islets of Langerhans] in the [pancreas]. Glucagon is produced by the alpha cells in these islets.

Chemistry
Glucagon is a short hormone, its peptide chain being made up of only 29 [amino acid]s. In solid form it looks like a white powder.
Molecular mass: 3483
Empirical Formula:C₁₅₃H₂₂₅N₄₃O₄₉S

Role in the Body
When blood glucose levels are too low [alpha] cells in the [islets of Langerhans] produce [proglucagon], which is processed into glucagon and released. This glucagon is carried through the [blood]stream and when it interacts with liver cells causes them to break down glycogen to glucose. [Glycogen] is normally stored within the [liver]. It provides a source of energy that can be acessed much more quickly than that of fat. As glycogen is broken down the level of glucose in the blood increases, and the secretion of glycogen ceases. Glucagon also encourages the breakdown of fats, and their increased use within the body.

Glycogen production is also stimulated by eating a lot of protein. This is why there are some high-protein diets that are supposedly effective. If glucagon secretion remains high then less of the energy taken in in food should be stored as [fat] or [glycogen].

Glucagon and the [diabetes|Diabetic]
Glucagon is not needed in the daily regime of [diabetics], but should be available in case of emergency [hypoglycemia]. If a diabetic falls unconscious it isn't possible to raise their blood-[sugar] level by feeding them, so unless an [intravenous] drip is available then an injection of glucagon is the only way to quickly raise this level and prevent [brain] damage or death. The glucagon in these kits is produced by [transgenic] Escherichia coli bacteria.

Sources:
Biology 2
Collins Medical dictionary
www.glucagon.com

glucagon (thing)