Blood vessels — Cambridge IGCSE Biology
The structure and functions of arteries, veins and capillaries, and the main blood vessels to and from the heart, lungs, kidneys and liver.
Revision notes
2 short notes, in the order of the specification. Each one in short:
Arteries carry blood away from the heart at high pressure, so they have thick walls with muscle and elastic fibres and a narrow lumen. Veins carry blood back at low pressure, with thin walls, a wide lumen and valves to stop backflow. Capillaries have walls one cell thick and are the site of exchange between blood and tissues.
The main blood vessels are the vena cava, which brings deoxygenated blood from the body to the right atrium, the pulmonary artery to the lungs, the pulmonary vein back to the left atrium, and the aorta to the body. The renal artery and vein serve the kidneys, and the hepatic portal vein carries absorbed nutrients to the liver.
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Quick check questions
Which blood vessels have valves?
Show answer
Veins.
State the function of capillaries.
Show answer
Exchange of substances between the blood and the cells of the body tissues.
Supplement Why do arteries have thick walls?
Show answer
They carry blood at high pressure, so the walls must withstand it.
Name the blood vessel that carries blood from the lungs to the heart.
Show answer
Pulmonary vein.
Supplement Which vessel carries blood from the small intestine to the liver?
Show answer
The hepatic portal vein.
Frequently asked questions
Why do arteries have thick elastic walls?
Supplement Arteries have thick walls containing muscle and elastic fibres because they carry blood away from the heart at high pressure. The thick walls withstand the pressure, and the elastic fibres let the walls stretch and recoil with each heartbeat. The narrow lumen helps to maintain the pressure as the blood travels to the organs.
Why do veins have valves but arteries do not?
Supplement Veins have valves because they carry blood back to the heart at low pressure, and the valves stop the blood flowing backwards. Arteries carry blood away from the heart at high pressure and do not have valves. Veins also have thin walls and a wide lumen, giving little resistance to flow.
What blood vessels carry blood away from the heart?
Arteries carry blood away from the heart, and veins return it to the heart. The aorta carries oxygenated blood from the left ventricle to the body, and the pulmonary artery carries deoxygenated blood from the right ventricle to the lungs. Arteries do not always carry oxygenated blood: the name depends on direction.
How are capillaries adapted for exchange?
Supplement Capillaries have walls only one cell thick, giving a short distance for diffusion, and their walls are permeable, so substances in the plasma can leak out and pass in. They are very narrow and form a large network close to every cell, and the slow flow of blood gives time for exchange.
Written and checked against the Cambridge IGCSE Biology (0610) specification · Updated October 2026