blood vessels

• what is the role of arteries?

  these carry the blood away from the heart.
• what is the role of capillaries?

  these are involved in the exchange of materials at the tissues.
• what is the role of veins?

  these carry blood to the heart.
• why are artery walls strong and elastic?

  the heart pumps the blood out a high pressure.
• what do arteries branch into?

  capillaries
• what is the structure of capillaries?

  • they are tiny, too small to see.
  • they are very narrow.
  • they have permeable walls.
  • their walls are usually 1 cell thick.
• why are capillaries very narrow?

  so they can squeeze into gaps between cells, meaning they can carry blood really close to every cell in the body to exchange substances with them.
• why do capillaries have permeable walls?

  so substances can diffuse in and out.
• why are capillaries only 1 cell thick?

  It increases the rate of diffusion by decreasing the distance over which it occurs.
• what do capillaries supply?

  food and oxygen, and take away waste like carbon dioxide.
• what do capillaries eventually join up to form?


  veins
• why is the blood at lower pressure in the veins?

  so the walls don't need to be as thick as artery walls.
• why do veins have a bigger lumen than arteries?

  to help the blood flow despite the lower pressure.
• why do veins have valves?

  to help keep the blood flowing in the right direction.
• why do arteries contain thick layers of muscle?

  to make them strong and elastic fibres allow them to stretch and spring back.
• what is the structure of arteries?

  • the walls are thick compared to the size of the lumen (hole down the middle).
  • they contain thick layers of muscle and elastic fibres.
• what adaptations do arteries have for their function?

  • the walls have elastic fibres allowing them to stretch and spring back.
  • artery walls have thick layers of muscle making them strong and able to cope with the high pressure at which blood is pumped by the heart.
• what type of blood do the arteries carry?

  oxygenated blood
• Which is the only artery that doesn't carry oxygenated blood?

  pulmonary artery
• when are veins formed?

  when capillaries join up after passing through the body.
• what type of blood do veins carry?

  they transport deoxygenated blood (apart from the pulmonary vein) from the organs back to the heart.
• how are veins adapted to their function?

  • thin walls as the blood is at a lower pressure
  • low blood pressure hinders flow so veins have a wider cross section through which blood can flow to counteract this.
  • they have valves to prevent the backflow of blood.
• how are veins different from arteries?

  • veins have valves, arteries do not
  • veins have a wider cross section
  • vein walls are thinner
• in capillaries, why can there be an efficient exchange of waste products and food + oxygen?

  they have thin walls and pass very closely to the body cells.
• due to capillaries' adaptations, what can there be an efficient exchange of?

  • waste products, such as carbon dioxide, move out of the cells and into the blood.
  • food and oxygen move out of the blood and into cells.
• what do arteries branch into?

  capillaries
• why do veins have valves?

  to prevent the backflow of blood