Your heart pumps blood around your entire body, but the heart muscle is living tissue too. It needs its own continuous supply of oxygen and nutrients in order to keep contracting. That supply comes from a special set of blood vessels called the coronary arteries.
Coronary heart disease becomes easier to understand once you see it as a simple supply problem. If the coronary arteries become narrowed, less blood can reach the heart muscle. If one becomes completely blocked, the affected part of the heart muscle may be starved of oxygen long enough to become damaged.
Try these five questions before reading the chapter. They will show you which ideas you already understand and which ones need more attention.
- 5 diagnostic questions
- Focus on the essential CHD concepts
- Instant explanation for every answer option
1. The Heart Needs Its Own Blood Supply
The heart contains a thick layer of muscle called cardiac muscle. These muscle cells contract continuously throughout your life, so they require a steady supply of energy.
Like other actively respiring cells, cardiac muscle cells require oxygen and nutrients. The oxygen is needed for aerobic respiration, which releases the energy required for muscular contraction.
The blood inside the chambers of the heart is not the main source of oxygen for the heart muscle. The heart muscle receives its blood supply through the coronary arteries.
Coronary arteries arise near the beginning of the aorta and run over the surface of the heart, branching to supply different regions of cardiac muscle.
This distinction is important. The heart pumps blood, while the coronary arteries carry blood to the heart muscle. An artery itself does not pump blood.
2. What Is Coronary Heart Disease?
Coronary heart disease (CHD) occurs when the coronary arteries become narrowed or blocked so that the blood supply to the heart muscle is reduced.
The word occlusion means obstruction or blockage of a blood vessel. This is a particularly useful word to recognise because CHD is described in the syllabus in terms of the occlusion of coronary arteries.
Atherosclerosis and plaque formation
One important process leading to CHD is atherosclerosis. Fatty material, including cholesterol-containing deposits, accumulates within the wall of an artery and forms a plaque.
As the plaque becomes larger, it projects further into the passage through which blood flows. This passage is called the lumen.
Wide lumen: blood can flow relatively freely through the coronary artery.
Narrowed lumen: blood flow is restricted, so less oxygenated blood can reach the heart muscle.
Occluded lumen: blood flow may be stopped, depriving part of the heart muscle of oxygen.
Follow the cause-and-effect sequence
| Stage | What happens? | Effect on the heart muscle |
|---|---|---|
| 1. Fatty plaque develops | Material accumulates in the coronary artery wall. | The lumen begins to become narrower. |
| 2. Lumen narrows | There is less space through which blood can flow. | Blood supply to the cardiac muscle is reduced. |
| 3. Oxygen delivery falls | Less oxygenated blood reaches the affected muscle. | Aerobic respiration is limited and the muscle cannot function as effectively. |
| 4. Severe or complete blockage | Blood flow to part of the heart muscle may stop. | Heart muscle cells can become damaged or die, causing a heart attack. |
Why does reduced blood flow matter so much?
Cardiac muscle cells are constantly active. If their oxygen supply falls, they cannot maintain aerobic respiration at the normal rate. This means less energy is made available for normal muscular contraction.
If the blood supply is completely interrupted for long enough, the affected cardiac muscle cells become seriously damaged and may die. This is a heart attack, also called a myocardial infarction.
Narrowed coronary artery → reduced blood flow → reduced oxygen supply → less aerobic respiration in cardiac muscle → impaired heart muscle function.
Coronary heart disease is not exactly the same as a heart attack
| Coronary heart disease | Heart attack |
|---|---|
| A disease affecting the coronary arteries. | An acute event in which blood supply to part of the heart muscle is severely reduced or stopped. |
| Usually develops over time as coronary arteries become narrowed or obstructed. | Can occur when a coronary artery becomes critically or completely blocked. |
| Reduces blood flow to the heart muscle. | Can cause death of cardiac muscle cells. |
3. Risk Factors for Coronary Heart Disease
A risk factor is something that increases the probability of developing a disease. It does not mean that a person will definitely develop the disease.
For O-Level Biology, three particularly important lifestyle risk factors are unhealthy diet, sedentary lifestyle and smoking.
Unhealthy diet
A diet containing excessive amounts of saturated fat can contribute to an unhealthy blood cholesterol profile and increase the likelihood of fatty plaque developing in arteries. Over time, this can contribute to narrowing of the coronary arteries.
This does not mean that pieces of fat from food simply travel through the bloodstream and stick directly onto artery walls. The biological process is more complex. At O-Level, the key idea is that an unhealthy diet increases the risk of fatty deposits developing in the arteries.
Sedentary lifestyle
A sedentary lifestyle means doing very little physical activity. Regular physical activity helps maintain cardiovascular fitness and a healthy body mass.
Long-term physical inactivity is associated with conditions such as excess body fat, high blood pressure and an unhealthy blood lipid profile, all of which can contribute to increased cardiovascular risk.
Smoking
Smoking affects the cardiovascular system in several ways.
- Carbon monoxide binds strongly to haemoglobin, reducing the amount of oxygen that the blood can carry.
- Nicotine can increase heart rate and blood pressure, making the heart work harder.
- Other chemicals in tobacco smoke can damage the lining of arteries and contribute to the development of atherosclerosis.
Do not memorise “smoking is bad for the heart” as an isolated statement. Be able to explain why: smoking can reduce oxygen transport and damage the cardiovascular system, increasing the risk of coronary heart disease.
4. Preventing Coronary Heart Disease
Many important CHD risk factors are modifiable. In other words, lifestyle choices can reduce the probability of developing the disease.
| Risk factor | Why it increases risk | Preventive measure |
|---|---|---|
| Unhealthy diet | Can promote an unhealthy blood lipid profile and development of fatty deposits in arteries. | Eat a balanced diet and avoid excessive saturated fat. |
| Sedentary lifestyle | Increases cardiovascular risk and makes maintaining a healthy body mass more difficult. | Take part in regular physical activity. |
| Smoking | Reduces oxygen transport and damages the cardiovascular system. | Do not smoke or stop smoking. |
Notice that prevention questions are often closely linked to risk-factor questions. If inactivity is a risk factor, regular exercise is a sensible preventive measure. If smoking is a risk factor, avoiding smoking reduces that risk.
When you state a preventive measure, connect it to the risk factor it reduces. This makes your answer biologically meaningful rather than simply listing unrelated “healthy habits”.
Common Mistakes
| Common mistake | What you should say instead |
|---|---|
| “The coronary arteries pump blood to the heart.” | The heart pumps blood. The coronary arteries carry oxygenated blood to the heart muscle. |
| “Coronary arteries supply blood to the whole body.” | The coronary arteries specifically supply the cardiac muscle. |
| “CHD is the same thing as a heart attack.” | CHD is disease of the coronary arteries. A heart attack can occur when the blood supply to part of the heart muscle becomes severely reduced or blocked. |
| “Fat from food simply sticks directly onto the inside of an artery.” | An unhealthy diet can increase the risk of atherosclerotic plaque forming in artery walls. The process is not simply undigested dietary fat sticking to the vessel. |
| “The plaque blocks the heart chamber.” | CHD involves narrowing or blockage of the lumen of a coronary artery. |
| “The only problem is that less glucose reaches the heart.” | The most important consequence is reduced oxygen delivery, which limits aerobic respiration in cardiac muscle. |
| “Exercise cleans fat out of the arteries.” | Regular exercise helps reduce cardiovascular risk; it does not simply scrub plaque from artery walls. |
| “Eating sugar directly causes coronary arteries to become blocked.” | For the syllabus, focus on an unhealthy diet, particularly excessive saturated fat, alongside sedentary lifestyle and smoking as important lifestyle risk factors. |
What You Should Be Able to Do
Know the structures and terms
- State the function of the coronary arteries.
- Define occlusion in the context of a coronary artery.
- Recognise that the lumen is the space through which blood flows.
- Explain what is meant by atherosclerosis and plaque formation.
Explain how CHD develops
- Describe how plaque can narrow a coronary artery.
- Link a narrower lumen to reduced blood flow.
- Link reduced blood flow to reduced oxygen delivery.
- Explain why reduced oxygen limits aerobic respiration in cardiac muscle.
- Explain how complete occlusion can result in a heart attack.
Apply the risk-factor ideas
- State unhealthy diet as a possible CHD risk factor.
- State sedentary lifestyle as a possible CHD risk factor.
- State smoking as a possible CHD risk factor.
- Give appropriate preventive measures for each modifiable risk factor.
- Distinguish a risk factor from a guaranteed cause of disease.
These ten questions test whether you can connect coronary artery structure, blood flow, respiration, risk factors and prevention rather than simply memorising definitions.
- 10 mastery questions
- Exam-focused cause-and-effect reasoning
- Instant explanation for every answer option
FAQ
Frequently Asked Questions About Coronary Heart Disease
Once the main cause-and-effect sequence is clear, a few common questions help connect the ideas and prevent typical examination mistakes.
What exactly does “occlusion” mean?
Occlusion means blockage or obstruction. In coronary heart disease, occlusion of a coronary artery restricts or prevents blood from reaching part of the heart muscle.
Why does the heart need coronary arteries when there is already blood inside it?
Blood inside the chambers is being pumped through the circulatory system. The thick cardiac muscle forming the wall of the heart requires its own blood vessels to deliver oxygen and nutrients directly to its cells. The coronary arteries provide this supply.
What is the difference between narrowing and complete occlusion?
A narrowed artery still has a lumen through which some blood can flow, although the flow may be restricted. With severe or complete occlusion, blood flow through the affected vessel may stop, creating a much greater risk of damage to the heart muscle.
Is coronary heart disease the same as a heart attack?
No. Coronary heart disease describes disease that reduces blood flow through the coronary arteries. A heart attack is an acute event in which the blood supply to part of the heart muscle is severely reduced or cut off long enough to damage or kill cardiac muscle cells.
Does eating fat mean fat simply sticks to the inside of an artery?
No. That explanation is too simplistic. The development of atherosclerosis involves changes within the artery wall and the formation of plaque. For O-Level Biology, the important link is that an unhealthy diet, especially one containing excessive saturated fat, can increase the risk of atherosclerosis and coronary heart disease.
Why is oxygen so important when explaining CHD?
Cardiac muscle cells need oxygen for aerobic respiration. If a coronary artery becomes narrowed or blocked, less oxygen reaches the affected muscle. Aerobic respiration is therefore limited and the muscle may no longer function normally. Prolonged oxygen deprivation can cause cardiac muscle cells to die.
How does smoking increase the risk of CHD?
Smoking affects the cardiovascular system in several ways. Carbon monoxide reduces the oxygen-carrying capacity of the blood, nicotine can increase heart rate and blood pressure, and other chemicals in tobacco smoke can damage blood vessel walls. Together, these effects increase cardiovascular risk.
Can exercise simply remove plaque that is already inside an artery?
No. It is misleading to imagine exercise physically “cleaning” an artery. Regular physical activity helps reduce cardiovascular risk and improves overall cardiovascular health, which is why it is an important preventive measure.
What should I write if an exam asks for causes and prevention of CHD?
Start with the major lifestyle risk factors highlighted in the syllabus: unhealthy diet, sedentary lifestyle and smoking. Then match each with a sensible preventive measure: eat a balanced diet with less excessive saturated fat, take regular exercise and avoid smoking.
Coronary heart disease becomes much easier to remember when you follow one continuous chain: coronary artery narrowing or occlusion → reduced blood supply → reduced oxygen delivery → less aerobic respiration in cardiac muscle → possible heart muscle damage. Once that sequence is clear, the causes and preventive measures fit naturally around it rather than becoming a list of facts to memorise.