Applied Anatomy and Physiology - Cardiovascular system - A-Level Physical Education

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Applied Anatomy and Physiology - Cardiovascular system

infoWhy this? The Cardiovascular System unit is taught at the start of Year 12 because it builds on students’ prior GCSE knowledge of the heart, blood vessels and circulation, while introducing the more detailed physiological concepts required at A Level. Understanding how oxygen, nutrients and other substances are transported around the body provides a foundation for studying exercise physiology and performance.

scheduleWhy now? This unit supports later learning on energy systems, the body's responses to exercise, and adaptations to training, as students need to understand how the cardiovascular system works both at rest and during physical activity. Introducing this topic early helps students develop key physiological principles that can be applied throughout the course.

Heart rate is the number of times the heart beats each minute and is measured in beats per minute; a typical resting value is approximately 60–80 beats per minute.
Stroke volume is the volume of blood ejected by the left ventricle per beat and is approximately 70 millilitres at rest.
Cardiac output is the volume of blood ejected by the left ventricle each minute and is approximately 5 litres per minute at rest.
Cardiac output is calculated using `Q = HR \times SV`, where cardiac output is usually expressed in litres per minute, heart rate in beats per minute and stroke volume in litres per beat.
Heart rate can be measured by counting an arterial pulse for a fixed period and converting it to beats per minute, while stroke volume can be calculated using `SV = Q / HR`.
The cardiac cycle is one complete heartbeat and consists of diastole, when the heart relaxes and fills with blood, and systole, when cardiac muscle contracts.
During atrial systole, the atria contract to complete ventricular filling; during ventricular systole, the ventricles contract and eject blood into the pulmonary artery and aorta.
The heart is myogenic because the cardiac muscle can generate its own electrical impulses without stimulation from a motor nerve.
The sinoatrial node, or SA node, is the heart's natural pacemaker and initiates an impulse that spreads across the atria, causing atrial systole.
The atrioventricular node, or AV node, briefly delays the impulse so that the ventricles can finish filling before they contract.
The impulse travels from the AV node down the Bundle of His and through the Purkinje fibres, causing ventricular systole from the apex upwards.
As exercise intensity increases, heart rate rises approximately linearly towards its maximum, stroke volume rises and usually plateaus during submaximal exercise, and cardiac output increases substantially.
During recovery, heart rate and cardiac output gradually decrease towards resting values, while stroke volume may remain temporarily elevated to support oxygen delivery, heat loss and waste removal.
Venous return is the flow of blood back to the heart, and increased venous return raises ventricular filling and stroke volume through the Frank–Starling mechanism.
The muscle pump increases venous return when contracting skeletal muscles compress veins, while pocket valves prevent the blood from flowing backwards.
The respiratory pump increases venous return because deeper breathing creates pressure changes between the abdomen and thorax that draw blood towards the heart.
Sympathetic venoconstriction contracts smooth muscle in vein walls, reducing venous capacity and helping return more blood to the heart during exercise.
The cardiac control centre in the medulla oblongata receives information from chemoreceptors, baroreceptors and proprioceptors and adjusts heart rate through the autonomic nervous system.
Sympathetic stimulation through the cardiac accelerator nerve and the hormone adrenaline increase SA node activity, whereas parasympathetic stimulation through the vagus nerve decreases heart rate.
The vascular shunt mechanism redistributes cardiac output by vasodilating arterioles and opening pre-capillary sphincters supplying active muscles and skin, while vasoconstricting vessels supplying less active organs; the vasomotor centre coordinates these changes through sympathetic nervous activity.

rocket_launchYou must be able to

Calculate cardiac output using `Q = HR \times SV`, converting stroke volume from millilitres to litres when the answer is required in litres per minute.
Rearrange the cardiac output equation to calculate heart rate using `HR = Q / SV` or stroke volume using `SV = Q / HR`.
Calculate heart rate from a pulse count by dividing the number of beats by the measurement time in seconds and multiplying by 60.
Sequence the cardiac cycle by describing diastole, atrial systole and ventricular systole, including the movement of blood through the atria and ventricles.
Trace an electrical impulse from the SA node through the AV node, Bundle of His and Purkinje fibres, linking each stage to atrial or ventricular contraction.
Analyse exercise data to explain how heart rate, stroke volume and cardiac output change from rest to submaximal exercise, maximal exercise and recovery.
Explain how the muscle pump, respiratory pump, pocket valves and venoconstriction alter venous return and affect stroke volume through the Frank–Starling mechanism.
Explain changes in heart rate by linking receptor information to the cardiac control centre, sympathetic or parasympathetic nerves, and hormonal stimulation.
Analyse the redistribution of cardiac output by linking the vasomotor centre to vasodilation, vasoconstriction, arterioles and pre-capillary sphincters.

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