A non-communicable disease: Students should understand the consequences of…

The idea

Heart valves are flap-like structures that keep blood flowing one way through the heart. The atrioventricular valves sit between atria and ventricles, and the semilunar valves sit between ventricles and the arteries leaving the heart. When a valve is faulty, it may not close fully, so blood leaks backwards, or it may become narrowed, so blood is forced through a smaller opening. Either problem means the heart must work harder to move the same volume of blood, which can cause breathlessness, tiredness, dizziness and swelling from fluid retention. A common example is a leaky mitral valve allowing blood to flow back into the left atrium during ventricular contraction.

What earns the marks

• Valves normally prevent backflow by closing between contractions, so blood travels in one direction through the heart.
• A faulty valve may fail to close completely, allowing blood to leak backwards, or may be narrowed, restricting forward flow.
• Backflow or restricted flow reduces the efficiency of the heart, so the heart must contract more forcefully or more often.
• Consequences can include breathlessness, tiredness, dizziness, fainting and swelling caused by fluid retention.
• The extra workload can lead to further heart problems, and severe cases may require treatment such as valve replacement.

Common mistakes and how to put them right

• Thinking that a faulty valve stops blood flowing altogether.

  Put it right: The error is ignoring that leakage or narrowing usually reduces rather than blocks flow, so the correction is to describe reduced efficiency and backflow.

• Confusing the direction of leakage, for example saying blood leaks from the atrium into the ventricle when the atrioventricular valve fails.

  Put it right: Blood leaks backwards from the ventricle into the atrium.

• Assuming faulty valves only affect the heart and not the rest of the body.

  Put it right: Link poor circulation to symptoms such as breathlessness, tiredness and swelling.

Exam tips

• Name the valve and the chamber or vessel on each side of it so your description of backflow is precise.
• Use the phrase one-way flow and explain what happens when it is not maintained.
• Link each consequence to the extra work done by the heart rather than listing symptoms without explanation.