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During a game of football, a player’s heart rate will vary.
a) Explain how changes in the acidity of the blood cause the heart rate to increase
during a game of football. (4 marks)
b) Years of training will eventually result in football players having a lowered resting
heart rate. What term is used to describe a resting heart rate that is below 60
beats per minute? (1 mark)
c) How does a lower resting heart rate affect oxygen delivery to muscles? (2 marks)
a)
* Increase in blood acidity caused by increase in CO2 and lactic acid levels.
* Detected by chemoreceptors (in carotid arteries).
* Nerve impulse sent to cardiac centre in medulla oblongata.
* Nerve stimulation to SAN decreases vagal and increases sympathetic impulses to
increase heart rate.
b)
* Bradycardia.
c)
* Stroke volume increases due to cardiac hypertrophy.
* Resting cardiac output remains constant so oxygen delivery is maintained.
* Cardiac hypertrophy results in less O2 requirement from heart and therefore more
available for working muscles.
Performers will often use running as part of their training programme. Both
heart rate and stroke volume increase when running.
(a) Use 'Starling's law of the heart' to explain how stroke volume increases
when running. (3 marks)
(b) Explain how the heart controls the rate at which it beats. (4 marks)
a)
* Starling’s Law states that the greater venous return, the greater stroke
volume is.
* As venous return increases the walls of the ventricles are stretched further.
* Results in a more powerful contraction.
* Increases the amount of blood pumped around the body during exercise.
b)
* Increases in blood acidity detected by chemoreceptors.
* Chemoreceptors located in carotid arteries.
* Nerve impulses sent to cardiac centre in medulla oblongata.
* Stimulate the SAN via the vagal (to decrease HR) and sympathetic (to
increase HR) nerves.
a)
b)
c)
Briefly explain the terms ‘cardiac output’and ‘stroke volume’, and the relationship
between them. (3 marks)
Explain the term cardio-vascular drift. (3 marks)
Explain how it is possible for a trained performer and an untrained performer to
have the same cardiac output for a given workload.(2 marks)
a)
* Cardiac output is the volume of blood leaving left ventricle per minute.
* Stroke volume is the volume of blood leaving left ventricle per beat.
* Stroke volume x heart rate = cardiac output.
b)
* Increase in heart rate that occurs during prolonged exercise.
* Occurs to compensate for decreased stroke volume in order to maintain cardiac
output.
* This is caused by reduction in fluid in blood due to sweating.
* This increases blood viscosity and decreases venous return (and thus stroke volume
through Starling’s Law).
c)
* Trained athelte will have larger stroke volume.
* Can therefore achieve same cardiac output with lower heart rate.
* Untrained athlete compensates for smaller stroke volume by increasing heart rate.
When a gymnast is performing, the physical demands of exercise will cause
changes to the gymnast’s cardiac output and stroke volume.
a) What are the effects of training on resting ‘cardiac output’ and ‘stroke
volume’? (2 marks)
b) Explain how rising levels of carbon dioxide cause an increase in cardiac
output. (4 marks)
a)
* Training causes cardiac hypertrophy which leads to greater stroke volume.
* Resting cardiac output remains the same.
* Resting heart rate decreases due to increased stroke volume.
b)
* Increase in blood acidity caused by increase in CO2 and lactic acid levels.
* Detected by chemoreceptors (in carotid arteries).
* Nerve impulse sent to cardiac centre in medulla oblongata.
* Nerve stimulation to SAN decreases vagal and increases sympathetic
impulses to increase heart rate.
* Results in an increased cardiac output.
When participating in a sporting activity the physical demands of exercise
are met by increasing blood flow to some areas of the body.
a) What are the effects of training on resting cardiac output, heart rate
and stroke volume? (3 marks)
b) Both heart rate and stroke volume increase during exercise. What
causes the increase in stroke volume? (2 marks)
a)
* Training causes cardiac hypertrophy which leads to greater stroke
volume.
* Resting cardiac output remains the same.
* Resting heart rate decreases due to increased stroke volume.
b)
* Starling’s Law states that the greater venous return, the greater stroke
volume is.
* As venous return increases the walls of the ventricles are stretched
further.
* Results in a more powerful contraction.
* Increases the amount of blood pumped around the body during exercise.
Describe how the sinoatrial node (SAN) and the atrioventricular
node (AVN) control the increase in heart rate during exercise. (6
marks)
* Impulse for cardiac contraction initiated by SAN.
* SAN found in wall of right atrium.
* SAN sets heart’s rhythm and also known as pacemaker.
* SAN causes atria to contract.
* Impulse passes to AVN.
* Then travels down septum in the Bundle of His.
* Reaches tip of ventricle and branches out through purkinje
fibres.
* Delay in the impulse before AVN causes ventricles to contract.
* Heart rate controlled by autonomic nervous system.
* Parasympathetic branch decreases HR via vagus nerve.
* Sympathetic branch increases HR via sympathetic nerve.

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