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.
Arteries and veins carry blood around your body. Arteries take blood away from your heart, delivering it to your organs and muscles. Veins bring blood back to your heart from those same organs and muscles. Your main arteries include the coronary arteries of your heart, the carotid and cerebral arteries of your brain, and the peripheral arteries, which stretch out into your limbs.