Interesting Facts About Brain

The brain consumes up to twenty percent of the energy used by the human body, more than any other organ. Brain metabolism normally relies upon blood glucose as an energy source, but during times of low glucose (such as fasting, exercise, or limited carbohydrate intake), the brain will use ketone bodies for fuel with a smaller need for glucose. The brain can also utilize lactate during exercise. Long-chain fatty acids cannot cross the blood–brain barrier, but the liver can break these down to produce ketones. However the medium-chain fatty acids octanoic and heptanoic acids can cross the barrier and be used by the brain. The brain stores glucose in the form of glycogen, albeit in significantly smaller amounts than that found in the liver or skeletal muscle.
Although the human brain represents only 2% of the body weight, it receives 15% of the cardiac output, 20% of total body oxygen consumption, and 25% of total body glucose utilization. The need to limit body weight has led to selection for a reduction of brain size in some species, such as bats, who need to be able to fly. The brain mostly uses glucose for energy, and deprivation of glucose, as can happen in hypoglycemia, can result in loss of consciousness. The energy consumption of the brain does not vary greatly over time, but active regions of the cortex consume somewhat more energy than inactive regions: this fact forms the basis for the functional brain imaging methods PET and fMRI. These are nuclear medicine imaging techniques which produce a three-dimensional image of metabolic activity.