Describe the structure of arteries, veins and capillaries and explain its relation to function

ArteriesArteries carry blood away from the heart. They have a thick muscular wall with a small lumen. The thick muscular walls withstands the high pressure of the blood flowing from the heart.
VeinsThe veins are responsible for returning the blood to the heart. They have a thinner wall compared to arteries, and have a large lumen. The veins contain valves preventing back flow.
Capillaries
The capillaries are the smallest, with a thin, semi-permeable wall and a very small lumen. This allows blood to pass through one cell at a time. Their semi-permeable wall allows for the transport of gases and nutrients into and out of the blood.