Final answer:
Glycogen stored in the liver helps in maintaining blood glucose levels during fasting or the postabsorptive state, a process facilitated by glycogenolysis. The liver is crucial in regulating blood glucose levels by breaking down glycogen into glucose, which is released into the bloodstream, especially important when dietary glucose is not available.
Step-by-step explanation:
Glycogen stored in the liver can be used to increase blood glucose levels if they fall, as they would during fasting. Glycogen is a polymer of glucose and serves as an important energy storage molecule in animals. When there is surplus energy, excess glucose is converted into glycogen for storage predominantly in the liver and muscle tissues. During periods without food intake, such as fasting, the body relies on these glycogen stores to maintain a balanced blood glucose level, a state known as the postabsorptive or fasting state.
When blood sugar levels begin to drop, glycogen stored in the liver can be readily hydrolyzed into glucose 1-phosphate (G-1-P), which is then transformed into glucose 6-phosphate (G-6-P) and enters the glycolytic pathway to produce ATP. This process is called glycogenolysis. The liver's role is especially crucial as it helps in maintaining the blood glucose levels for the entire body, whereas muscle glycogen is primarily used for glycolysis within muscle cells during vigorous exercise.
In the postabsorptive state, as glucose levels fall, the hormone insulin decreases, and another hormone called glucagon is released. Glucagon stimulates the liver to break down glycogen into glucose, thereby preventing hypoglycemic conditions. Thus, the liver's storage and release of glucose are essential for energy homeostasis and are pivotal during fasting or when the body is not receiving a regular intake of food.