Describe how different types of blood vessel are structurally adapted for their purpose.

Arteries, carrying blood away from the heart have a thick muscular wall that is more elastic than fibrous tissues. This is elastic to cope with the high fluid pressure in the lumen and allows distention and resultant propagation of a pulse wave. The lumen is relatively small and largely clear, valves are only found in the proximal aorta and pulmonary artery.Veins, carry blood back towards the heart. They have a much thinner wall than arteries, comprising mostly fibrous tissue, which is more protective. The lumen is quite large and the blood is under comparatively lower pressure. Due to the pressure drop, veins have regular semi-lunar valves to maintain a unidirectional flow of blood.Capillaries, are the smallest blood vessels with a diameter of only 7-10 µm. Their endothelium is only one cell thick and therefore they have no muscle, elastic or fibrous tissue. Due to their massive surface area the blood is under very low pressure.