Veins and Arteries
Veins are vessels that return blood to the heart. Blood pressure is very low in veins because blood is being returned to the heart. They contain one-way valves that prevent the back-flow of blood. Venules are small veins.
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Arteries are vessels that carry blood away from the heart to the lungs to become oxygenated. Arteries resist the pressure of blood from the heart. Arteries also contain a thicker layer of smooth muscle than veins. The second largest artery is the pulmonary trunk.
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