CHD: A Non-Communicable Disease (AQA GCSE Biology: Combined Science)

• The heart is made of cardiac muscle cells which need a supply of blood to deliver oxygen, glucose (for respiration) 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 and sit on the outside of the heart

The coronary arteries supply the heart with oxygenated blood

What is coronary heart disease?

• Coronary heart disease (CHD) involves layers of fatty material (called plaque) building up inside the coronary arteries
• If a coronary artery becomes partially or completely blocked by these fatty deposits blood flow through the arteries is reduced 
• This results 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

Buildup of plaque in the coronary arteries narrows the lumen

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

• Treatment of CHD involves either:
  • increasing the width of the lumen of the coronary arteries using a stent
  • 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

• 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

Advantages and Disadvantages of Stents

Inserting a stent diagram

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

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:

Advantages and Disadvantages of Statins

• The heart valves play a vital role in ensuring blood is pumped from the ventricles to the arteries, in a one-way direction
• In some people, heart valves may become faulty as a result of illness, old age or a heart attack
• Valves can stiffen which can prevent them from 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 back into the atria or the arteries back into 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
  • mechanical valves

Advantages and Disadvantages of Replacement Valves

• In the case of heart failure a heart can be transplanted from a donor who has recently died
• Waiting lists for organ transplants are often long, so an immediate solution can involve replacing the heart with an artificial heart made from plastic and metal
• Artificial hearts may be used to:
  • keep patients alive while waiting for a heart transplant, 
  • allow the heart to rest as an aid to recovery

Advantages and Disadvantages of Artificial Hearts