Liver glycogen fuel reserve

The fuel reserves of a healthy adult human are of three types glycogen stored in the liver and, in relatively small quantities, in muscles large quantities of triacylglycerols in adipose tissues and tissue proteins, which can be degraded when necessary to provide fuel (Table 23-5). 

The main stores of glycogen in the body are found in skeletal muscle, where they serve as a fuel reserve for the synthesis of ATP during muscle contraction, and in the liver, where glycogen is used to maintain the blood glucose concentration, particularly during the early stages of a fast. 

Under normal conditions, the processes shown in Figure 3-2 are tightly coupled, so that the oxidation of metabolic fuels is controlled by the availability of ADI which, in turn is controlled by the rate at which ATP is being utilized in performing physical and chemical work. Work output, or energy expenditure, thus controls the rate at which metabolic fuels are oxidized, and hence the amount of food that must be eaten to meet energy requirements. As discussed in section 5.3.1, metabolic fuels in excess of immediate requirements are stored as reserves of glycogen in muscle and liver and as fat in adipose tissue. 

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