Blood/ circulatory system

• 1. Capillaries are the smallest of the three blood vessels.
  2. The role of capillaries is to exchange nutrients and waste products with the tissues.
  3. Capillary walls are permeable, meaning substances are able to move through them.
  4. Their walls are also only one cell thick which means a short distance for diffusion.
  5. Capillaries carry blood at a low pressure and have a lower rate of flow than arteries.
• 1. The role of veins is to carry blood from the body (or lungs) back to the heart.
  2. Veins are a similar size to arteries, but they have relatively thin walls and a relatively wide lumen
  3. This is because they carry blood at a much lower pressure.
  4. Veins also contain valves to prevent the blood from flowing backwards.