Brain energy requirements

The brain and other areas of the central nervous system (CNS) have high ATP requirements. Although the brain only represents about 2% of the body s mass, it consumes around 20% of the metabolized oxygen and ca. 60% of the glucose. The neurons high energy requirements are mainly due to ATP-de-pendent ion pumps (particularly Na7K " AT-Pase) and other active transport processes that are needed for nerve conduction (see p. 350). 

The brain relies on the circulation for nutrients and is a chief consumer of glucose. The brain uses about 15 percent of the energy required for minimal maintenance of body functions (called the basal metabolic rate). Brain tissue doesn t store energy. Instead, the brain must rely on the circulation for its fuel supply. Not all molecules can be transported across the blood-brain barrier to be used for energy. One molecule that can cross the blood-brain barrier is glucose, the preferred fuel source for the brain. Brain tissue can also adapt to ketone bodies such as acetoacetate as a source of fuel. 

Tissues with particularly high oxygen and energy requirements, including the brain and heart, are particularly susceptible to harmful effects resulting from reduced levels of oxygen in the body. 

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