Describe how the structure of arteries, veins and capillaries is adapted to their functions in the human circulatory system.

Arteries have thick walls made of smooth muscle and elastic tissue, allowing them to withstand and maintain the high pressure of blood pumped from the heart.

Arteries carry oxygen‑rich blood away from the heart, so their thick walls prevent bursting under high pressure.

Veins have thinner walls with less muscle and elastic tissue because the blood pressure in veins is low.

Veins contain valves that prevent backflow of blood, ensuring it moves towards the heart.

Capillaries have very thin walls and a small lumen, which reduces the diffusion distance and allows efficient exchange of gases, nutrients and waste between the blood and tissues.