Glycogen serves as the body’s primary storage form of glucose, crucial for maintaining stable energy levels. The liver plays a central role, acting as a significant reservoir for stored glucose. This stored energy is readily available to be released into the bloodstream when the body requires it.
Glycogen and Its Purpose in the Liver
Glycogen is a large, branched molecule made up of many individual glucose units linked together. The liver stores a substantial amount of glycogen to regulate blood glucose levels for the entire body. This function is particularly important for organs that rely heavily on a constant supply of glucose, such as the brain, which consumes a significant portion of the body’s glucose even at rest.
The liver’s role in glycogen storage differs from muscle glycogen. While muscles also store glycogen, their stores are primarily used as a local fuel source for contraction during physical activity. In contrast, the liver acts as a central glucose dispenser, breaking down its glycogen to release glucose into circulation, ensuring all tissues and organs have access to the energy they need, especially during periods without food intake.
Liver Glycogen Storage Limits
The adult human liver typically stores 80 to 120 grams of glycogen, equivalent to approximately 320 to 480 calories of readily available energy. For an adult weighing approximately 70 kg, liver glycogen can constitute about 5-6% of the liver’s fresh weight.
Storage capacities vary among individuals, influenced by several factors. Dietary carbohydrate intake is a primary determinant; consuming a diet rich in carbohydrates can help maximize liver glycogen stores. Physical activity levels also play a role, as exercise depletes glycogen, and subsequent carbohydrate intake helps replenish these stores.
Overall health status, including liver health and insulin sensitivity, affects the liver’s ability to synthesize and store glycogen. Insulin resistance, for example, can impair the liver’s capacity for glycogen synthesis. Individual metabolic differences also contribute to variations.
How Liver Glycogen is Used
When blood glucose levels begin to fall, the liver initiates a process called glycogenolysis. This involves the breakdown of its stored glycogen into glucose. The liver then releases this glucose directly into the bloodstream.
This release of glucose helps maintain stable blood sugar levels, providing a continuous energy supply to vital organs. The hormone glucagon, secreted by the pancreas in response to low blood glucose, stimulates glycogenolysis in the liver. Glucagon signals the liver to break down glycogen, ensuring a steady supply of glucose.