What Are the Structures and Functions of Capillaries and Veins?
Capillaries are tiny blood vessels where the smallest arteries meet the smallest veins and where the blood exchanges food and oxygen for waste products. Veins, which are also blood vessels, return depleted blood to the heart.
Some capillaries are so small that they can only be seen under a microscope, and tiny blood cells can only pass through them one at a time. Because capillaries are so small, their walls are correspondingly thin. Nutrients carried by the blood are able to pass through these walls to the cells of the body. Waste materials from the cells and tissues can also pass through the walls and be carried away. In the lungs, the capillaries exchange oxygen and carbon dioxide.
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