Blood Vessels

• There are three different types of blood vessels:

  1. Arteries - these carry blood away from the heart.
  2. Capillaries - these are involved in the exchange of materials at the tissues.
  3. Veins- these carry the blood to the heart.
• The heart pumps blood out at high pressure so the artery walls are strong and elastic.
• The walls of arteries are much thicker compared to the lumen - the hole down the middle.
• Arteries contain thick layers of muscle to make them strong, and elastic fibres to allow them to stretch and spring back.
• Arteries branch into really tiny capillaries that are too small to see with the human eye.
• Capillaries carry blood really close to every cell in the body to exchange substances with them.
• Capillaries have permeable walls, so substances can diffuse in and out and they not only supply food and oxygen but also take away waste like CO2.
• Capillary walls are usually only one cell thick. This increases the rate of diffusion by decreasing the distance over which it occurs.
• Capillaries eventually join up to form veins. The blood is at lower pressure in the veins so the walls don't need to be as thick as artery walls.
• Veins have bigger lumen than arteries to help the blood flow despite the lower pressure.
• Veins have valves to help keep the blood flowing in the right direction.
• 1464ml of blood passed through an artery in 4.5mins. If you calculate the rate of blood flow through the artery in ml/min, the answer would be 325ml/min because the rate of blood flow = volume of blood/number of minutes therefore the rate of blood flow = 1464/4.5 which = 325ml/min.