How does the cardiovascular system deliver oxygen to the muscles, and how does it respond to exercise?
The structure and function of the heart, the pathway of double circulation, heart rate, stroke volume and cardiac output, and the role of the blood vessels.
A focused answer to the WJEC GCSE PE topic on the cardiovascular system, covering the structure and function of the heart, double circulation, the definitions and link between heart rate, stroke volume and cardiac output, and the role of arteries, veins and capillaries.
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What this dot point is asking
WJEC wants you to describe the structure and function of the heart, the pathway of double circulation, the meaning and link between heart rate, stroke volume and cardiac output, and the role of the blood vessels.
Structure and function of the heart
The left side of the heart is more muscular than the right because it pumps blood all the way around the body, while the right side only pumps to the nearby lungs.
Double circulation
The human circulatory system is a double circulation, meaning blood passes through the heart twice on each full circuit:
- Pulmonary circulation: the heart pumps deoxygenated blood to the lungs, where it picks up oxygen and returns to the heart.
- Systemic circulation: the heart pumps oxygenated blood to the body (including the working muscles), where it delivers oxygen and returns deoxygenated.
This keeps oxygenated and deoxygenated blood separate and delivers oxygen efficiently.
Heart rate, stroke volume and cardiac output
These three terms describe how much blood the heart moves.
They are linked by the equation:
During exercise, both heart rate and stroke volume rise, so cardiac output rises, delivering more oxygen to the muscles.
The blood vessels
Three types of blood vessel carry blood around the body.
- Arteries: carry blood away from the heart at high pressure; thick, muscular walls; carry oxygenated blood (except the pulmonary artery).
- Veins: carry blood back to the heart at low pressure; thinner walls with valves to prevent backflow; carry deoxygenated blood (except the pulmonary vein).
- Capillaries: tiny vessels with one-cell-thick walls where gas exchange happens, delivering oxygen to the muscles and removing carbon dioxide.
The functions of blood
Blood does more than carry oxygen, and these jobs all matter during exercise:
- transports oxygen from the lungs to the muscles (carried by red blood cells) and carbon dioxide back to the lungs,
- transports nutrients such as glucose to the muscles for energy,
- removes waste products such as lactic acid from the muscles,
- regulates body temperature by carrying heat to the skin, where it is lost through sweating and a reddened skin.
How the cardiovascular system responds to exercise
When a performer exercises, the cardiovascular system works harder to meet demand:
- heart rate rises so blood is pumped more often,
- stroke volume rises so more blood is pumped per beat,
- cardiac output rises (more blood and oxygen per minute to the muscles),
- blood is redirected towards the working muscles and skin and away from organs such as the gut (this is called the vascular shunt).
Why this matters
The cardiovascular system works with the respiratory system to supply oxygen for aerobic exercise, and it is the system that responds most clearly to training, with a lower resting heart rate and a larger stroke volume as long-term effects. Heart rate is also the basis of the training zones used to set intensity.
Exam-style practice questions
Practice questions written in the style of WJEC exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
WJEC style3 marksDefine heart rate, stroke volume and cardiac output, and state how they are linked.Show worked answer →
A 3-mark question: a mark for the definitions and a mark for the link (the equation).
Heart rate is the number of times the heart beats per minute. Stroke volume is the volume of blood pumped out of the heart in one beat. Cardiac output is the volume of blood pumped out of the heart in one minute.
They are linked by the equation cardiac output equals heart rate multiplied by stroke volume. So if either heart rate or stroke volume rises (as in exercise), cardiac output rises, delivering more blood and oxygen to the working muscles.
WJEC style4 marksDescribe the role of arteries, veins and capillaries in the cardiovascular system.Show worked answer →
A 4-mark question: reward a correct role for each vessel, with credit for a structural feature.
Arteries carry blood away from the heart, usually at high pressure; they have thick muscular walls to cope with the pressure and carry oxygenated blood (except the pulmonary artery). Veins carry blood back to the heart at low pressure; they have thinner walls and valves to stop blood flowing backwards, and carry deoxygenated blood (except the pulmonary vein). Capillaries are tiny vessels with very thin (one-cell-thick) walls where gas exchange takes place, allowing oxygen to pass into the muscles and carbon dioxide to pass into the blood.
Markers reward the direction of flow for arteries and veins, the role of valves, and gas exchange at the capillaries.
Related dot points
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Sources & how we know this
- WJEC GCSE Physical Education specification (from 2016) — WJEC (2016)