50.19 Regulating Glucose Levels in the Blood Insulin and glucagon maintain the homeostasis of circulating glucose.
of the cells of the body preferentially use fatty acids as their metabolic fuel. One tissue that does not switch fuel sources during the postabsorptive period is the nervous system.
The cells of the nervous system require a constant supply of glucose, and they do not require the action of insulin to enable them to take up glucose from the blood. The nervous system can use other fuels only to a very limited extent. The overall dependence of neuronal tissue on glucose is the reason it is so important for other cells of the body to shift to fat metabolism during the postabsorptive period. This shift preserves the available glucose and glycogen stores for the nervous system for as long as possible.
The traffic of fuel molecules during the absorptive and postabsorptive periods is summarized in Figure 50.20, which indicates the steps controlled by insulin and glucagon.
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