Heart Rate & Exercise (Edexcel IGCSE Biology: Double Science)
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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)
- 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
- Other factors can also influence the heart rate, such as the hormone adrenaline
Exercise and heart rate
- The heart pumps blood around the body in order to supply oxygen and glucose to respiring cells
- The blood also removes waste products from the respiring cells
- During exercise, the cells of the muscles respire more rapidly in order to provide energy for muscle contraction
- Respiration may be aerobic if exercise is moderate, or anaerobic if exercise is more intense
- An increase in respiration means an increase in requirement for oxygen and glucose as well as an increase in production of waste products that need to be removed
- The nervous system responds to this requirement by stimulating the following changes
- Heart rate increases to deliver oxygen and glucose and remove waste more frequently
- The volume of blood pumped out of the heart also increases to deliver bigger quantities of oxygen and glucose
- Production of the hormone adrenaline increases heart rate as part of a 'fight or flight' response
- At the end of a period of exercise, the heart rate may remain high for a period of time as oxygen is required in the muscles to break down the lactic acid from anaerobic respiration
- This is how the oxygen debt is paid off
- The time taken for the heart rate to return to the resting rate is called the recovery time
- A physically fit person will have a lower resting heart rate and a shorter recovery time compared to an unfit person
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