Heart Rate & Exercise (Edexcel IGCSE Biology)

Spec point — 2.66 · explain how the heart rate changes during exercise and under the influence of adrenaline

Heart Rate & Exercise

Control of the heart rate

• A heart rate is measured by counting the number of times a heart beats in a minute (bpm)

  • Factors such as exercise or levels of adrenaline can affect a heart rate

• The natural resting heart rate is controlled by a group of cells located in the right atrium called the pacemaker

  • The role of the pacemaker is to coordinate the contraction of the heart muscle and regulate the heart rate
  • Pacemaker cells send out electrical impulses which initiate a contraction in the cardiac muscle

Exercise and heart rate

• The heart pumps blood to respiring cells to supply oxygen and glucose for respiration and to remove carbon dioxide

• During exercise, muscle cells respire faster to release more energy for contraction

  • During intense exercise, anaerobic respiration may occur when oxygen supply is insufficient to meet the energy needs of muscle cells
  • Aerobic respiration (respiration with oxygen) is still occurring in the muscle cells at the same time

• Increased respiration increases the demand for oxygen, glucose, and for the removal of carbon dioxide

• The nervous system responds by:

  • Increasing heart rate to deliver more oxygen and glucose and remove carbon dioxide more quickly
  • Increasing the **volume of blood **pumped per heart beat, so more blood reaches the muscles per minute

• After exercise, the** heart rate** remains high for a period of time to supply oxygen needed to break down lactic acid produced during anaerobic respiration (repaying the oxygen debt)

• The hormone adrenaline also increases heart rate as part of the ‘fight or flight’ response, preparing the body for action