Arteries carry blood away from the heart. Blood enters them in surges each time the ventricles contract, so the blood is at high pressure and the pressure rises and falls with each heartbeat. Most arteries carry oxygenated blood; the pulmonary artery is the exception, carrying deoxygenated blood from the right ventricle to the lungs.The structure of an artery is adapted to this high, pulsing pressure:Thick wall. The wall is thick compared with the lumen, so it can withstand high pressure without bursting.Many elastic fibres in the middle layer. When the ventricles contract, the surge of blood stretches the wall. When the ventricles relax, the elastic fibres recoil, pushing the blood onwards. This evens out the flow and keeps the pressure up between beats. You can feel this stretching and recoil as the pulse, for example at the wrist.
Smooth muscle in the middle layer helps to maintain the wall's strength and can alter the diameter of the vessel.Collagen in the outer layer resists overstretching, so the wall does not balloon or burst under pressure.Folded endothelium. The inner lining is folded, so the lumen can expand when a surge of blood passes. The endothelium is smooth, which reduces friction.Narrow lumen. A relatively small lumen helps keep the blood at high pressure.The largest arteries, such as the aorta, have the most elastic tissue because they receive blood directly from the heart.
Smooth muscle in the middle layer helps to maintain the wall's strength and can alter the diameter of the vessel.Collagen in the outer layer resists overstretching, so the wall does not balloon or burst under pressure.Folded endothelium. The inner lining is folded, so the lumen can expand when a surge of blood passes. The endothelium is smooth, which reduces friction.Narrow lumen. A relatively small lumen helps keep the blood at high pressure.The largest arteries, such as the aorta, have the most elastic tissue because they receive blood directly from the heart.