Exercise and your arteries
More than 300 years ago, the great English physician Thomas Sydenham observed, "A man is as old as his arteries." It's as true today as it was then. And in a 21st-century update on 17th-century wisdom, we might add that your health is only as good as your arteries, since these blood vessels carry vital oxygen-rich blood to all your body's tissues.
Your heart's job is to pump blood to all parts of your body. The main pumping chamber, the left ventricle, delivers blood to the aorta, the largest and strongest of the arteries. Like the limbs of a tree, the aorta divides into arteries that grow progressively smaller as they branch from the main trunk. Ultimately, the smallest arteries lead into capillaries, the tiny vessels with filmy walls only one cell thick that allow oxygen to pass freely to the tissues while collecting carbon dioxide and other waste products that pass into the blood for disposal by the lungs, kidneys, and liver.
Exercise changes the way your circulation distributes blood to your body. Your digestive tract, liver, and kidneys get less blood, but your exercising muscles get much more as millions of capillaries open up to feed the muscle cells. As you overheat, the blood flow to your skin increases as well. Like your exercising muscles, your heart needs more oxygen, so it gets more blood. But even though exercise is a smart thing to do, your brain's blood flow remains relatively constant.