A patient has a blocked coronary artery. Explain why a blockage in a coronary artery is dangerous and describe how the heart's double circulatory system normally ensures that the body tissues receive enough oxygen.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Coronary heart disease occurs when fatty deposits build up inside the coronary arteries, reducing blood flow to the heart muscle. It is one of the leading causes of death in the UK.
Model answer (5 marks)
A blockage in a coronary artery is dangerous because the coronary arteries supply the myocardium with oxygenated blood and glucose. If a plaque blocks the artery, the heart muscle cannot respire aerobically and therefore cannot receive enough oxygen, leading to loss of contractile function and a heart attack.
The heart’s double circulatory system has two separate circuits. The pulmonary circuit carries de‑oxygenated blood from the heart to the lungs, where it is oxygenated, and returns it to the heart. The systemic circuit then pumps this oxygenated blood from the heart to the body tissues at high pressure. This arrangement guarantees that body cells receive a continuous, adequate supply of oxygenated blood for aerobic respiration.
The heart’s double circulatory system has two separate circuits. The pulmonary circuit carries de‑oxygenated blood from the heart to the lungs, where it is oxygenated, and returns it to the heart. The systemic circuit then pumps this oxygenated blood from the heart to the body tissues at high pressure. This arrangement guarantees that body cells receive a continuous, adequate supply of oxygenated blood for aerobic respiration.
Examiner tips
- Use the exact terms ‘myocardium’, ‘oxygenated blood’, ‘double circulatory system’, ‘pulmonary circuit’, ‘systemic circuit’.
- Show the sequence: blockage → loss of oxygen → heart failure; double circuit → pulmonary → systemic → oxygen delivery.
- Keep the answer concise – 5 marks, so 1–2 sentences per point.
Mark scheme (5 marks)
- Coronary arteries supply the heart muscle (myocardium) with oxygenated blood / oxygen and glucose
- A blockage means the heart muscle cannot respire aerobically / cannot receive enough oxygen, so it stops beating properly / heart attack occurs
- The double circulatory system has two circuits: the pulmonary circuit (heart to lungs and back) and the systemic circuit (heart to body and back)
- Blood is oxygenated in the lungs and returned to the heart before being pumped at high pressure to the body tissues
- This ensures body tissues / cells receive a good / constant supply of oxygenated blood for aerobic respiration
Key terms in this question
coronary artery · double circulatory system
Related
- All Edexcel A-Level Biology A: Salters-Nuffield (9BN0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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