Glycogenolysis

At a certain moment no more glucose from the meal is left, and the body will have to find an other way of producing energy.
At this time the supplies of glycogen stored in the liver and the muscles will be used.

In a process that is called glycogenolysis the liver will re-create glucose from the glycogen that was stored in times of plenty.
This glucose will then be transported to the other organs, such as the brain, where it can be broken down for energy.
(The glycogen in the muscle can be broken down but not transported, so this is for personal use of the muscle only).

The brain is only capable of getting energy from glucose (fatty acids cannot enter the brain, and the brain can't create supplies). The brain is a mass consumer of the available glucose, so the supply of glycogen will not last very long. The supply is usually depleted after an overnight fast.

Read further: gluconeogenesis >