blood vessels 2.2.2

• there are three types of blood vessels

  • arteries which carry blood away from the heart
  • veins which carry blood into the heart
  • capillaries which are involved in the exchange of materials at the tissues
• the arteries have strong and elastic walls because the heart pumps blood out at high pressure
• the walls of the arteries are thick compared to the small size of the lumen because the blood is at high pressure
• the artery walls contain thick layers of muscle tissue to make strong to handle the high pressure
• the artery walls contain elastic fibres to allow them to stretch and spring back
• the vein walls are thinner than the artery walls because the blood is at lower pressure
• the veins have bigger lumen than arteries to help the blood flow despite the lower pressure
• the veins have smaller layers of elastic fibres and muscle
• the veins have valves to keep the blood flowing in the right direction and prevent backflow
• the capillaries are the smallest blood vessel and are too small to see
• capillaries carry the blood really close to every cell in the body to exchange substances with them
• capillaries have permeable walls, so that substances can diffuse in and out of them
• capillaries supply food and oxygen and take away wastes like CO2
• the capillary walls are usually only one cell thick which increases the rate of diffusion by decreasing the distance over which it occurs
• the capillaries have very small lumen which can only carry one red blood cell at a time
• arteries have a pulse whereas veins and capillaries dont
• arteries branch out into capillaries
• capillaries eventually join up to form veins
• a pulse is a rhythmical throbbing of the artery as the blood is propelled through them
• the rate of blood flow = volume of blood / number of minutes