|MadSci Network: Anatomy|
First, let me tell you that your body has more than just veins. You also have arteries and capillaries. I think the answer you are seeking is to the question: "How many miles of blood vessels are there in a human body?"
The arteries are the vessels that carry blood from the heart to the organs and tissues of the body. They begin at the base of the heart and branch like tree trunks (hollow ones, of course) until they get smaller and smaller. Finally, when they reach the tissue cells of the body, they are so tiny that only one blood cell can get through them at a time. When the blood vessels are this small they are called capillaries. There are more capillaries (and more miles of capillaries) than any other kind of blood vessel.
Veins are the vessels that drain the blood from the capillaries and carry it back to the heart. The tiny veins that drain the capillaries flow into larger and larger vessels, like a river flowing to the sea. When they deliver the blood back to the heart the heart pumps the blood back to the arteries and it begins its round trip again.
To answer your question, there are approximately 60,000 miles of blood vessels in an adult human body. That's about 100,000 kilometers. And if you really did stretch out your vessels for 60,000 miles most of them would be capillary miles. Each capillary is very short, but there are so very many of them.
I found the answer to your question in a college textbook of human anatomy and physiology. The title is "Human Anatomy and Physiology", Third Edition, by Elaine N. Marieb. It is published by The Benjamin/Cummings publishing Company, Inc., which is headquartered in Redwood City , California. The copyright date is 1995. The answer is on p. 643, the first page of the chapter on blood vessels.
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