Blood Vessels

• Arteries

  Carry blood away from the heart to the rest of the body
• Arteries


  Carry blood away from the heart to the various organs of the body
• Arteries


  • Have a really thick muscular wall containing lots of elastic tissue which allows them to stretch and recoil as the heart beats, helping maintain high pressure
  • Wall contains connective tissue and fibres of collagen to prevent overstretching and protect from pressure
  • Inner lining (endothelium) is folded which allows the artery to expand (elastic recoil) and withstand high pressure
  • Small lumen ensures a high pressure is maintained
• Arterioles


  Smaller vessels that distribute blood from arteries to capillaries and places of high demand
• Arterioles


  • Contain smooth muscle which can contract to restrict blood flow or relax to allow full blood flow, directing blood to parts of the body in higher oxygen demand
• Capillaries


  The smallest blood vessels that are the site of molecule exchange between blood and tissue fluid
• Capillaries


  • Have a narrow diameter of 7µm which reduces blood flow to allow time for exchange between blood and surrounding cells, increasing efficiency
  • Are one cell thick to ensure maximum rate of transfer between blood and surrounding tissue fluid
  • Have pores in the walls to allow plasma and dissolved substances to leave the blood
• Venules


  Larger than capillaries but smaller than veins, allow deoxygenated blood to return from capillary beds to larger blood vessels called veins
• Venules


  • Have thinner walls than arterioles made out of muscle, elastin and collagen
  • Are porous to allow fluid and blood to easily move through their walls
  • Range from 8 to 100μm in diameter
• Veins


  Consist of an outer layer of connective tissue with fibres of collagen, have a thin wall with little elastic fibres and smooth muscle
• Veins


  • Blood flows under low pressure which means that the blood flow in veins is helped by the contraction of body muscles surrounding them
  • Have no pulse so don't need to contract or recoil
  • Have pocket valves that prevent backflow