Glucagon and Liver Glucose Output In Vivo

Human survival is dependent on maintaining a constant supply of fuel to various tissues of the body. During periods of feasting, ingested nutrients are stored in the liver, fat, and muscle. In between meals, and in periods of fasting, these substrates can be either used locally or distributed to different tissues for consumption. Of the various energy substrates available, glucose is perhaps the most important since it plays a crucial and essential role with regard to nervous tissue. Under most circumstances, the liver is the only organ which releases glucose into the circulation for distribution to other tissues. This glucose is derived from either glycogen stores within the liver (glycogenolysis) or from de novo synthesis of glucose (gluconeogenesis).