What is the primary function of glycogen in the liver and muscle?

Glycogen primarily serves as a quick energy reserve in the liver and muscles. It is a polysaccharide that acts as a form of stored carbohydrate, readily accessible for energy needs during periods of physical activity or fasting. When the body requires energy, glycogen can be rapidly broken down into glucose, which is then utilized by cells for fuel.

In the liver, glycogen provides a critical source of glucose for maintaining blood sugar levels, especially between meals or during exercise when immediate energy is needed. In muscle tissue, the glycogen stored there is primarily used to meet the energy demands of muscle contractions during physical activity. This quick mobilization of energy from glycogen is crucial for sustained physical performance and effective metabolism.

Other options present functions that are not directly related to glycogen. While amino acids are important for building proteins, glycogen does not serve that role. Fat metabolism is a separate process primarily involving fatty acids and lipids, and bile production occurs in the liver but is unrelated to glycogen's role in energy storage and release.