Final answer:
In the liver, glycogen stores glucose in a polysaccharide form and is released into the bloodstream to maintain energy levels, particularly during fasting states such as overnight. After 12-18 hours without food, these glycogen stores start to deplete.
Step-by-step explanation:
In the liver, the glycogen is stored in the polysaccharide state to release glucose as needed. It gets depleted during prolonged fasting states after 12-18 hours.
Glycogen is a storage form of glucose which is made up of glucose monomers and is found in both liver and muscle cells. In the absorptive state, which is when the body is digesting food, liver cells convert excess glucose into glycogen for storage. However, in the postabsorptive state, or fasting state, when there is no food intake, the body relies on this stored glycogen for energy. Glycogen stored in the liver is particularly important because it helps maintain blood glucose levels for the entire body, while muscle glycogen is used locally within muscles.
During fasting, such as overnight or when meals are skipped, blood glucose levels begin to decrease. This triggers the release of glucagon from the pancreas, which then promotes the breakdown of glycogen into glucose to be released into the bloodstream, a process called glycogenolysis. In cases where fasting is prolonged and glycogen stores are depleted, the body then turns to alternative sources such as fatty acids and proteins for energy.