Revision notes for AQA GCSE Biology Coronary heart disease: a non-communicable disease. Open the guide for explanations and worked examples. Written against the AQA GCSE Biology (8461) specification, so the content matches what's examinable rather than general Biology background.
Coronary heart disease: a non-communicable disease
What you'll learn
- What coronary heart disease is and why it reduces oxygen supply to the heart muscle.
- How stents and statins are used to treat coronary heart disease.
- What happens when heart valves become faulty, and how they can be replaced.
- How to evaluate drugs, mechanical devices and transplants as treatments for cardiovascular disease.
Big picture: diseases of the heart and blood vessels
A disease is a condition that affects the normal functioning of part of the body. Some diseases are caused by pathogens, such as bacteria or viruses, but this topic is about diseases that are not spread between people.
Definition
Non-communicable disease
A non-communicable disease is a disease that cannot be passed from one person to another. It is often long-term and can be linked to lifestyle, genetic and environmental factors.
Cardiovascular disease means disease of the heart and blood vessels. Coronary heart disease is one important example.
Your heart is made of muscle tissue. Like all muscle, it needs oxygen and glucose for aerobic respiration, which releases energy for contraction.
The heart muscle needs its own blood supply
Even though the heart is full of blood, the heart muscle cannot rely on blood inside the chambers to supply it directly. The muscle wall is too thick for enough oxygen and glucose to diffuse through from the inside.
Instead, the heart muscle is supplied by the coronary arteries. An artery is a blood vessel that carries blood away from the heart, usually under high pressure. The coronary arteries branch over the surface of the heart and deliver oxygen-rich blood to the heart muscle cells.
Common Mistake
Blood inside the heart is not enough
Do not say the blood inside the heart chambers “feeds” the heart muscle directly. The heart muscle gets its oxygen and glucose from the coronary arteries.
Coronary heart disease
Definition
Coronary heart disease
Coronary heart disease is a cardiovascular disease in which layers of fatty material build up inside the coronary arteries, narrowing them and reducing blood flow to the heart muscle.
The fatty material contains substances such as cholesterol, a type of lipid. Cholesterol is needed by the body in small amounts, but high levels in the blood increase the risk of fatty deposits forming in arteries.
The space inside a blood vessel is called the lumen. In coronary heart disease, the lumen becomes narrower, so less blood can pass through. This means less oxygen reaches the heart muscle.
If the heart muscle receives less oxygen, it cannot carry out aerobic respiration as quickly. This means less energy is released for contraction. In severe cases, part of the heart muscle may die because its blood supply is blocked; this is a heart attack.
Key Idea
Cause-and-effect chain
Fatty material builds up → coronary arteries narrow → blood flow decreases → less oxygen reaches the heart muscle → less aerobic respiration → the heart muscle cannot contract properly.
Example
Explaining reduced oxygen supply
- The affected blood vessels are the coronary arteries, which supply the heart muscle with oxygen-rich blood.
- Fatty material narrows the lumen, so less blood can flow through the artery in a given time.
- Because blood carries oxygen, reduced blood flow means less oxygen reaches the heart muscle cells.
- With less oxygen, the rate of aerobic respiration decreases, so less energy is released for muscle contraction.
Treating coronary heart disease
Treatments for cardiovascular disease can involve drugs, mechanical devices or sometimes transplants. You need to be able to evaluate these by comparing benefits and risks.
Stents: keeping coronary arteries open
A stent is a small mesh tube inserted into a narrowed artery to keep it open. In coronary heart disease, stents are used to keep coronary arteries open so blood can flow more easily to the heart muscle.
Stents are mechanical devices. They can be very effective because they physically widen the narrowed artery.
Advantages of stents:
- They improve blood flow through the coronary artery.
- They can relieve symptoms quickly.
- They reduce the risk of a heart attack caused by that narrowed artery.
- They are a long-term treatment and do not require a donor organ.
Disadvantages of stents:
- Inserting a stent involves a medical procedure, so there are risks such as infection, bleeding or damage to the artery.
- Blood clots can form around the stent.
- The artery may narrow again.
- A stent does not lower blood cholesterol or stop fatty material forming elsewhere.
Statins: reducing blood cholesterol
Statins are drugs used to reduce blood cholesterol levels. Lower cholesterol slows down the rate at which fatty material is deposited in the arteries.
Statins are usually taken regularly over a long period of time. They are often used to reduce the risk of further cardiovascular disease.
Advantages of statins:
- They reduce blood cholesterol levels.
- They slow the build-up of fatty material in arteries.
- They can reduce the risk of heart attacks and strokes.
- They do not involve surgery.
Disadvantages of statins:
- They must be taken regularly, often for many years.
- They can cause side effects, such as muscle pain or liver problems in some people.
- They do not quickly open an artery that is already badly narrowed.
- Their effect depends on the patient taking them correctly.
Common Mistake
Statins and stents are different
A stent opens up an already narrowed artery. A statin lowers blood cholesterol to slow down future fatty deposits. Do not describe them as doing the same job.
Example
Choosing between a stent and statins
- If a coronary artery is already severely narrowed, the immediate problem is poor blood flow to the heart muscle. A stent directly tackles this by holding the artery open.
- If the patient also has high blood cholesterol, there is an ongoing risk of more fatty material being deposited. Statins reduce cholesterol and slow this process.
- The stent has the benefit of improving blood flow quickly, but it involves a procedure and has risks such as clotting or infection.
- Statins are useful for long-term risk reduction, but they take time to work and may cause side effects.
- A balanced judgement could be that the stent treats the immediate narrowing, while statins help reduce future risk.
Faulty heart valves
Heart valves are flaps of tissue that make sure blood flows in one direction through the heart. They open to let blood through, then close to stop blood flowing backwards.
In some people, heart valves become faulty. This can happen in two main ways:
- The valve may not open fully, so blood flow is restricted.
- The valve may develop a leak, so blood flows backwards.
If a valve does not open fully, the heart has to work harder to push blood through the smaller opening. If a valve leaks, some blood flows backwards, so less blood is pumped forwards with each heartbeat.
Either problem makes the heart less efficient. This can reduce oxygen delivery around the body and may cause tiredness, breathlessness or chest pain.
Example
Predicting the effect of a leaky valve
- A normal valve closes after blood passes through, preventing blood from flowing backwards.
- If the valve leaks, some blood returns in the wrong direction during each heartbeat.
- This means the volume of blood pumped forwards is reduced, so less oxygen may be delivered to body tissues.
- The heart may try to compensate by beating harder or faster, which can make the person feel tired or breathless.
Replacing faulty valves
Faulty heart valves can be replaced using biological valves or mechanical valves.
A biological valve is made from human or animal tissue. It works more like a natural valve, but it may wear out and need replacing later.
A mechanical valve is made from artificial materials. It can last a very long time, but blood clots may form on it, so the patient may need to take anti-clotting drugs.
Both types require surgery, so there are risks such as infection, bleeding and problems linked to anaesthetic.
Heart failure and transplants
Heart failure means the heart cannot pump enough blood around the body. It does not mean the heart has completely stopped, but it does mean the heart is not working well enough for the body’s needs.
In severe heart failure, a patient may need a heart transplant. A transplant is an operation where a damaged organ is replaced with a healthy donor organ. Sometimes a heart and lungs transplant is needed if both organs are seriously damaged.
Advantages of a heart transplant:
- It can greatly improve quality of life.
- It may save the patient’s life when other treatments are not enough.
- A successful donor heart can work much better than the failing heart.
Disadvantages of a heart transplant:
- Donor hearts are in short supply.
- It is major surgery, so it carries serious risks.
- The patient’s immune system may reject the donor heart.
- The patient must take immunosuppressant drugs, which reduce rejection but also increase the risk of infection.
An artificial heart is a mechanical pump used to keep blood circulating. Artificial hearts are used only occasionally. They may keep a patient alive while waiting for a donor heart, or allow the heart to rest as an aid to recovery.
Example
Evaluating an artificial heart
- In heart failure, the heart cannot pump enough blood, so tissues may not receive enough oxygen and glucose.
- An artificial heart can take over some or all of the pumping role, helping to maintain circulation.
- This is especially useful if the patient is waiting for a donor heart, because suitable donor organs may not be available immediately.
- However, an artificial heart requires surgery and can increase the risk of blood clots, bleeding and infection.
- A good judgement is that it may be worth the risk when the patient is in serious danger without it, but it is usually not a simple permanent cure.
Comparing treatment types
| Treatment type | Examples | Main benefit | Main risk or limitation |
|---|---|---|---|
| Drugs | Statins | Can reduce risk without surgery | Side effects; patient must keep taking them |
| Mechanical devices | Stents, mechanical valves, artificial hearts | Can physically improve blood flow or pumping | Surgery or procedures carry risks |
| Biological replacements | Biological heart valves | Can restore one-way blood flow | May wear out and need replacing |
| Transplants | Donor heart or heart and lungs | Can replace a failing organ | Donor shortage, rejection and major surgery risks |
Tip
How to evaluate treatments
Use this structure: benefit → risk → judgement. For example, “This treatment helps because…, however it may cause…, so it is most suitable when…”.
Exam technique
In the exam
- For coronary heart disease, write the cause-and-effect chain in order: fatty material, narrowed coronary arteries, reduced blood flow, less oxygen, less respiration in heart muscle.
- For evaluation questions, always include both benefits and risks, then make a clear judgement linked to the patient’s situation.
- Keep treatments distinct: stents open arteries, statins lower cholesterol, replacement valves restore one-way flow, and transplants or artificial hearts are used for severe heart failure.
Self review
Check yourself
- Why does narrowing of the coronary arteries reduce aerobic respiration in the heart muscle?
- How is the job of a stent different from the job of a statin?
- What are one advantage and one disadvantage of using a mechanical heart valve?
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