Glucagon and Glycogen
Glucose metabolism within a healthy human body goes like this: when food is consumed (especially carbohydrates) enzymes in the digestive system break down the compounds into sugars, which enter the bloodstream as the simple sugar (monosaccharide) glucose. As glucose builds up in the blood, the pancreas produces the hormone insulin which transports glucose to cells within the body to be used as energy immediately or stored for future use. Liver cells are especially important for storing unused glucose that otherwise would remain in the blood. Within the liver, glucose becomes stored as a complex sugar (polysaccharide) called glycogen.
This process of glucose absorption into cells leads to a drop in glucose within the blood. At a certain point, blood glucose levels are low enough that the pancreas starts producing another hormone, glucagon, whose function is to communicate to the liver cells to release certain amounts of stored sugar, which is done through receptors that convert glycogen back to glucose and release the glucose into the blood. As the stored sugar is released into the blood, blood glucose levels begin to rise, and cells throughout the body are provided with enough glucose to maintain proper function and energy.
So within a healthy human body, the functions of insulin and glucagon are essential and natural in regulating blood glucose levels and maintaining proper muscular and cognitive function.
Glucagon serves an additional function as well, which is to signal the release of stored fats within the liver through a process known as lipolysis. The release of stored fatty acids from the liver to be used by other tissues within the body, such as skeletal tissues, also helps maintain energy and glucose balance within the body. This particular function of glucagon is important for both healthy individuals and those with type 1 and advanced stages of type 2 diabetes.
When someone has type 1 diabetes, insulin is not produced properly by the cells of the pancreas and must be administered externally in order to metabolize glucose.
Type 2 diabetes usually occurs when the cells of the body stop responding properly to insulin, leading glucose to stay within the bloodstream. Individuals with prediabetes begin to exhibit these signs of insulin resistance, which if not addressed with dietary and lifestyle changes such as eating fresh whole foods and exercising, will often lead to type 2 diabetes. For those with advanced stages of type 2 diabetes, the pancreatic cells that produce insulin eventually become exhausted and stop functioning, and insulin must be administered externally in order to metabolize glucose.
Glucagon is also something of a safety-net for those with type 1, type 2 and prediabetes. Since typically glucose remains in the bloodstream of diabetics long after eating, there is rarely reason for glucagon to be produced by the pancreas in order to release stored sugars and raise blood glucose levels. When too much insulin is externally administered, however, glucagon must be produced in order to prevent hypoglycemia, a dangerous condition where blood sugar levels are too low.
Resources and Further Reading
An in-depth look at the history and metabolic functions of glucagon:
A look at carbohydrates and their impact of glucose metabolism:
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