Blood-brain barrier nutrient transport across

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. 

The SLC transporters mediate either drug uptake or efflux, whereas ABC transporters mediate only unidirectional efflux. Asymmetrical transport across a monolayer of polarized ceUs, such as the epithelial and endothelial cells of brain capillaries, is called vectorial transport (Figure 2-5). Vectorial transport is important in the efficient transfer of solutes across epithelial or endothelial barriers it plays a major role in hepatobiliary and urinary excretion of drugs from the blood to the lumen and in the intestinal absorption of drugs and nutrients. In addition, efflux of drugs from the brain via brain endothelial cells and brain choroid plexus epithelial cells involves vectorial transport. 

---