circulatory system and blood vessels

• name the three different blood vessels

  arteries, capillaries and veins
• arteries


  these carry blood from the heart
• capillaries

  these are involved in the exchange of materials at the tissues
• veins


  these carry blood to the heart
• arteries carry blood under pressure

  the heart pumps the blood out at a high pressure so the artery walls are strong and elastic. the walls are thick compared to the lumen. they contain thick layers of muscle to make them strong and spring back
• capillaries are really small


  arteries branch into capillaries. they carry blood really close to every cell to exchange substances with them. they supply food and oxygen and take away wastes like CO2. the walls are usually only one cell thick, this increases the rate of diffusion by decreasing the distance over which it occurs
• veins take blood back to the heart


  capillaries eventually join up to form veins the blood is carried at a lower pressure as they done need to be as thick. they have bigger lumen. they also have valves to help keep the blood flowing in the right direction