Lesson 7 of 7 / Transport in humans
Coronary arteries and heart disease
Why can a blocked coronary artery damage a heart that is full of blood?
I can connect coronary narrowing, reduced oxygen supply and risk factors.
I can explain coronary obstruction, risk factors and prevention.Syllabus
Syllabus K327 / K328, Topic 5(e). Explain coronary obstruction, risk factors and prevention.
About 4 min
Make a guess. You are not marked.
The heart is always full of blood. Why can a blocked artery on its surface still kill heart muscle?
Show the answer
Heart muscle gets oxygen from its own coronary arteries.
Blood inside the chambers does not feed the thick wall. A blocked coronary artery cuts oxygen to the muscle it supplies.
The key idea
Heart muscle needs its own coronary blood supply. An obstruction can reduce oxygen delivery and aerobic energy release.
Explanation
The blood inside heart chambers does not directly supply every muscle cell of the heart wall. Coronary arteries branch from the aorta and deliver oxygen and nutrients to the cardiac muscle through its own capillaries.
In coronary heart disease, fatty deposits can build up in coronary artery walls and narrow the lumen. A clot may form and obstruct the remaining space. Occlusion means blockage; narrowing can reduce flow before complete blockage occurs.
Reduced blood flow supplies less oxygen to the affected muscle. This limits aerobic respiration and the energy available for contraction. A severe or prolonged interruption can kill muscle cells, producing a heart attack.
Smoking, a sedentary lifestyle and diets high in saturated fat are risk factors. Smoking can damage artery linings, and some dietary patterns raise blood cholesterol, encouraging fatty deposits. These factors change risk rather than guaranteeing an outcome.
At the population level, avoiding smoking, regular physical activity and a balanced diet that limits saturated fat can reduce risk. These measures do not eliminate every cause: inherited factors and age can also influence risk.
Step by step
- 1
Locate the obstruction
Name a coronary artery supplying heart muscle, not just "the heart".
- 2
Trace the consequence
Narrower or blocked lumen -> less blood flow -> less oxygen delivered.
- 3
Explain the cell effect
Less aerobic respiration means less energy available for contraction; prolonged severe shortage can cause cell death.
Worked example
Explain an association carefully
A study finds more coronary disease among smokers. Give a biological explanation and one limit to the conclusion.
One way to explain it
Smoking can damage artery linings and contribute to narrowing or blockage of coronary arteries, reducing oxygen delivery to heart muscle. The association does not show that every smoker develops disease or that smoking is the only risk factor.
Why this answer works
- Connect the risk factor to the vessel.
- Connect reduced flow to oxygen supply.
- Avoid treating a risk factor as a certain prediction for an individual.
Watch out for this
A student says: "A coronary blockage stops oxygen entering the lungs." What is wrong with this?
Show the answer
It restricts blood supplying part of the heart muscle. Lung gas exchange is a different step in the oxygen-delivery pathway.
Check your understanding
What is the most direct effect of a blocked coronary artery on the muscle it supplies?
Show the answer
Less oxygen arrives, reducing aerobic energy release.
The muscle needs a continuing blood supply for respiration and contraction.
Exam-style questions
Check your understanding
A coronary artery is partly blocked by fatty deposits. Why can this cause chest pain during exercise?
Show the answer
Heart muscle gets too little oxygen for the aerobic respiration it needs
Less blood reaches the heart muscle, so it cannot release enough energy aerobically when working hard.
Quick recall
Why can a blocked coronary artery damage a heart that is full of blood?