AQA GCSE Biology

Revision Notes

2.4.1 CHD: A Non-Communicable Disease

CHD

Causes of CHD

  • The heart is made of cardiac muscle cells which like all cells in the body need a supply of blood to deliver oxygen, glucose and other nutrients and remove waste products such as carbon dioxide
  • The blood is supplied to the heart by the coronary arteries which branch off directly from the aorta
    • The heart needs to constantly respire, so it is vital that it receives oxygen

The coronary arteries, IGCSE & GCSE Biology revision notes

The coronary arteries supply the heart with oxygenated blood

  • In coronary heart disease (CHD), layers of fatty material build up inside the coronary arteries
  • These fatty deposits are mainly formed from cholesterol; of which there are two sources in the body:
    • Dietary cholesterol (from animal products eaten)
    • Cholesterol synthesised by the liver

 Buildup of plaque in the coronary arteries, IGCSE & GCSE Biology revision notes

Buildup of plaque in the coronary arteries narrows the lumen

Effect of narrowing of arteries, IGCSE & GCSE Biology revision notes

The effect of a narrowed lumen in a coronary artery is reduced blood flow to the heart

  • If a coronary artery becomes partially or completely blocked by these fatty deposits, it loses its elasticity and cannot stretch to accommodate the blood which is being forced through every time the heart contracts
  • This reduces the flow of blood through the arteries, resulting in a lack of oxygen for the heart muscle
    • Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina
    • Complete blockage means cells in that area of the heart will not be able to respire aerobically, leading to a heart attack
  • Treatment of CHD involves either increasing the width of the lumen of the coronary arteries using a stent, or prescribing statins to lower blood cholesterol

Treating CHD: Stents

  • Stents can be used to keep the coronary arteries open
    • A narrow tube is threaded up through the groin up to the blocked vessel
    • A tiny balloon is then inflated
    • The balloon pushes the metal or plastic stent against the wall of the artery, increasing the width of the lumen
    • The balloon and tube are then removed

 Inserting a stent into a blocked artery, IGCSE & GCSE Biology revision notes

Inserting a stent into a blocked artery is a relatively simple surgical procedure

  • Stents are very effective at reducing the risk of a heart attack as they widen the lumen to increase blood flow to the coronary arteries, and the procedure is relatively simple
  • Stents also last a long time, which is a positive, however, there is a risk of blood clots (thrombosis) occurring around

Treating CHD: Statins

  • Statins are drugs that are widely used to reduce the levels of fatty deposits (cholesterol) in the blood
  • They block an enzyme in the liver which is needed to make cholesterol
  • This slows down the rate of fatty material building up in the blood, reducing the risk of CHD occurring
  • There are many advantages and disadvantages of statins:

Statins advantages & disadvantages table

CHD_ A Non-Communicable Disease_1, downloadable IGCSE & GCSE Biology revision notes

Faulty Heart Valves

  • The heart valves play a vital role in ensuring blood is pumped from the ventricles to the arteries
  • In some people, heart valves may become faulty as a result of illness, old age or a heart attack
  • Valves can stiffer which can prevent them opening fully to let blood flow through
    • This reduces the volume of blood pumped by the heart
  • Sometimes a faulty heart valve might develop a leak
    • This allows blood to flow from the ventricles to the atria or the arteries to the ventricles
  • Both issues reduce the effectiveness of the heart in pumping oxygenated blood around the body
  • Faulty heart valves can be replaced via surgery using biological valves from cows or pigs, or mechanical valves

Exam Tip

You may be asked to evaluate different methods of treatment for CHD and faulty valves. You should bear in mind the benefits and risks associated with each type of treatment – there are always both as no treatment is perfect!

Heart Transplants

  • In the case of heart failure, a heart or heart and lungs for individuals with diseased lungs can be transplanted from a donor who has recently died
  • However, waiting lists for organs are long and not immediately available, so a short-term solution (or long-term solution if necessary) involves replacing the heart with an artificial one made from plastic and metal
    • They may be used to keep patients alive whilst waiting for a heart transplant, or to allow the heart to rest as an aid to recovery
  • The advantages of using artificial hearts are that there may be less of a wait for one to become available (as they are manufactured) and there is less chance of the patient’s immune system rejecting the artificial heart, but disadvantages are that artificial hearts don’t always work as well as real hearts at pumping blood around the body
    • As with stents, there is an increased risk of blood clots occurring around different parts of the artificial heart (which increases the likelihood of a stroke)
  • Faulty heart valves can be replaced via surgery using biological valves from cows or pigs, or mechanical valves

Exam Tip

You should be able to evaluate the advantages and disadvantages of treating cardiovascular diseases by drugs, mechanical devices or transplant. Issues to think about include: the risk of surgical procedures vs. the benefits of a successful outcome, the ease of access to the treatment and the potential side effects/long-term impacts.

Author: Jenna

Jenna studied at Cardiff University before training to become a science teacher at the University of Bath specialising in Biology (although she loves teaching all three sciences at GCSE level!). Teaching is her passion, and with 10 years experience teaching across a wide range of specifications – from GCSE and A Level Biology in the UK to IGCSE and IB Biology internationally – she knows what is required to pass those Biology exams.
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