Arteries | Veins | Capillaries |
Arteries are tough, thick and elastic tubes. | Veins are thin-walled and non-elastic tubes. | Capillaries are very thin-walled tubes. |
They have a narrow lumen. | They have a wide lumen. | They have a very narrow lumen, just wide enough for a red blood cell to pass through it. |
They carry blood away from the heart to the various organs of the body, at a high pressure. | They transport blood towards the heart from various organs, at a low pressure. | They carry blood from the arteries to the veins. |
They do not have valves. | They have valves to prevent backward flow of the blood. | They do not have valves. |
They transport only oxygenated blood (except for the pulmonary artery). | They transport only deoxygenated blood (except for the pulmonary vein). | They exchange oxygen, carbon dioxide, water and salts between the blood and the surrounding tissues. |