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.
The right side of the heart pumps blood to the lungs to pick up oxygen. The left side of the heart receives the oxygen-rich blood from the lungs and pumps it to the body. The heart has four chambers and four valves and is connected to various blood vessels. Veins are blood vessels that carry blood from the body to the heart. Arteries are blood vessels that carry blood away from the heart to the body. A Healthy Heart Cross-Section