What documents do I need to present to reenter the United States? If seeking to enter the United States after temporary travel abroad, you will need to present a valid, unexpired âgreen cardâ (Form I-551, Permanent Resident Card).
Brain Tour. 2. Supply lines. Your brain is nourished by one of your body's richest networks of blood vessels. With each heartbeat, arteries carry about 20 to 25 percent of your blood to your brain, where billions of cells use about 20 percent of the oxygen and fuel your blood carries. When you are thinking hard, your brain may use up to 50 percent of the fuel and oxygen.
A , Fitness, answered. To work at its best, the brain needs a constant supply of oxygen and glucose, which is carried to the brain by the blood. Because a constant supply of blood is so essential, the arteries supplying blood to the brain have the ability to narrow and widen as needed to ensure adequate oxygen and nourishment. Likewise, blood vessels within the brain widen and narrow to regulate the flow of blood to those areas of the brain working hardest.