biology

• Veins Always carry blood to the heart. Always carry deoxygenated blood, except for the pulmonary vein. Carry blood under low or negative pressure. Have thin walls - have less muscular tissue than arteries. Have a wide lumen. Veins contain valves which prevent the backflow of blood.
• The circulatory system consists of the heart, blood vessels (arteries, veins and capillaries) and blood. It transports nutrients, gases, hormones, heat and wastes around the body. It helps maintain homeostasis within the body.
• Arteries Always carry blood away from the heart. Carry oxygenated blood, except for the pulmonary artery. Carry blood under high pressure. Have thick muscular and elastic walls to pump and accommodate blood. The channel in the blood vessel that carries blood - the lumen - is narrow
• Veins Always carry blood towards the heart. Carry deoxygenated blood (except for the pulmonary vein). Carry blood at low pressure. Thinner than arteries as they do not need to withstand such high pressures.