Why do you think veins have valves
Answers
Answer:
Blood vessels may be tiny but they cover a lot of ground.
The smallest blood vessels measure only five micrometers. To give you some perspective, a strand of human hair measures about 17 micrometers.
But if you took all the blood vessels out of an average child and laid them out in one line, the line would stretch over 60,000 miles. An adult’s would be closer to 100,000 miles long.
There are three kinds of blood vessels: arteries, veins, and capillaries. Each of these plays a very specific role in the circulation process.
Arteries carry oxygenated blood away from the heart. They’re tough on the outside but they contain a smooth interior layer of epithelial cells that allows blood to flow easily. Arteries also contain a strong, muscular middle layer that helps pump blood through the body.
Veins have valves to prevent the back flow of blood. That is, that the blood flows in one direction and doesn't flows back
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