blood vessels

• Arteries


  Carry blood away from the heart
• Capillaries


  Exchange nutrients and oxygen with the tissues
• Veins


  Carry the blood back to the heart
• Arteries


  • Have a thick layer of muscle tissue to keep them strong
  • Have a thick layer of elastic tissue so they can stretch and recoil
• Capillaries


  • Have walls that are only a single cell thick
  • Are permeable, allowing substances to easily diffuse through them
  • Have a tiny lumen but a huge total cross-sectional area
• Veins


  • Have relatively large lumens
  • Have relatively thin walls with only small layers of elastic fibers and smooth muscle
  • Have valves to prevent blood from flowing backwards
• Blood flow through the circulatory system

  1. Blood is pumped from the heart into the arteries

  2. Blood flows through the capillaries and exchanges substances with the tissues

  3. Blood flows back to the heart through the veins
• The pressure of the blood is much lower in the capillaries than in the arteries, allowing for slower flow and better exchange of substances
• Calculating rate of blood flow


  Divide the volume of blood by the time it took to flow through