Giraffe have unusually high heart rates for their size, at 150 beats per minute. When the animal lowers its head the blood rushes down fairly unopposed and a rete mirabile in the upper neck, with its large cross sectional area, prevents excess blood flow to the brain. When it raises again, the blood vessels constrict and direct blood into the brain so the animal does not faint. The jugular veins contain several (most commonly seven) valves to prevent blood flowing back into the head from the inferior vena cava and right atrium while the head is lowered. Conversely, the blood vessels
Driving in the United States the flow of oxygen in the blood to the brain and other body parts. It affects people with heart disease and the central nervous system. Sulfur oxides are the cause of acid rain that damages the nature and human health. It particularly aggravates heart and lung diseases in children and the elderly. Nitrogen oxides are the main ingredients in the formation of acid rain and ground-level ozone that contributes to the global warming. Hydrocarbons are pollutants of air toxics and hazardous to the lung and other body parts. It causes cancer and birth defects. Finally, high-lead level in the air