cardiac and ventilation

• explain why it is necessary for the cardiac output of marathon runners to increase during a race(2)

  • to increase supply of oxygenated blood to muscles
  • to allow aerobic respiration
  • to provide more energy to meet increased demand
• deduce how adrenaline can cause a change in heart rate(4)

  • adrenaline is carried in blood
  • acts on the SAN
  • increasing frequency of impulses produced by SAN
  • increasing the rate the heart contracts
• explain how starting to excercise causes an increase in breathing rate(3)

  • excercise initiates impulses from stretch receptors in muscles
  • impulses sent to and from the ventillation centre in the medulla oblongata
  • leading to increase impulses to intercostal muscles or diaphragm
• explain the effect of exercise on the changes in oxygen consumption(4)

  • exercise will increase oxygen consumption
  • because there is more aerobic respiration occuring
  • because more energy(ATP) is needed by mucles
  • oxygen also required to convert lactate into glucose or pyruvate
  • oxygen consumption decreases after excercise
• describe how the SAN is involved in bringing about a change in heartrate as the level of activity increases(2)

  • more stimulation/depolarisation of SAN
  • causing more frequent waves of depolarisation from SAN to atria
  • leading to more frequent contraction of atria/stimulation of AVN