Organisation

• What is a Pacemaker?

  A group of cells in the right atrium that controls resting heart rate

  They produce small electrical impulses that spreads to the

  surrounding muscle cells
• What do valves do?

  Prevents blood flowing backwards.
• Describe the arteries.

  • Pump blood out at high pressure - strong and elastic walls
  • Thick walls - contain thick layers of muscle to make strong, elastic fibres - to allow them to stretch and spring back
• Describe the capillaries.

  • Very tiny
  • Carry blood really close to every cell to exchange substance with them
  • Permeable walls - substances can diffuse in and out
  • Supply food and oxygen - remove carbon dioxide
  • Thin wall - One cell thick
  • Thin wall increases rate of diffusion by decreasing distance
  • Small Lumen
• Describe the veins.

  • Pump blood out at lower pressure
  • Large lumen to help blood flow
  • Have valves to prevent backflow of blood
• How do you calculate the rate of blood flow?

  Rate of blood flow = Volume of blood / number of minutes