Blood Vessels (Cambridge O Level Biology)

Arteries

• Carry blood at high pressure away from the heart
• Carry oxygenated blood (other than the pulmonary artery)
• Have thick muscular walls containing elastic fibres
• Have a narrow lumen
• The speed of flow is fast

Veins

• Carry blood at low pressure towards the heart
• Carry deoxygenated blood (other than the pulmonary vein)
• Have thin walls
• Have a large lumen
• Contain valves (to prevent the backflow of blood)
• The speed of flow is slow 

Comparison of Arteries and Veins Diagram

Comparing arteries and veins

Capillaries

• Carry blood at low pressure within tissues
• Carry both oxygenated and deoxygenated blood
• Have walls that are one cell thick
• Have ‘leaky’ walls
• In some capillaries, the lumen is only wide enough for red blood cells to pass through in single-file
• The speed of flow is slow

Structure of a capillary