Cardiovascular disease

Cardiovascular disease

This topic is covered on both the GCSE and the A level spec. This tutorial is written for the A level standard. There are some difference between the exam boards and how they examine this. I will try to be a bit more specific about it later on in the tutorial. Cardiovascular disease is one of the major killers in modern times particularly in westernised countries such as USA and UK. In economically deprived countries it is not as significant killer. Infectious disease in these countries is still a major killer. Also, if you turn the clock back 100 years, infectious disease is a major killer. Cardiovascular diseases include a stroke and heart disease. A stroke is where the blood supply to the brain is cut off and so part of the brain dies. This normally leads to paralysis down one side of the body. Heart disease is where the coronary arteries become blocked. This means that the heart muscle is  deprived of oxygenated blood. As a result part of the heart muscle dies and this is when a heart attack occurs. We need to look at how the blood supply to both the heart and the brain becomes blocked off. This tends to occur over time. See the diagram below to show an overview of the stages.

Stages of atherosclerosis

Image was supplied by Alila Medical Media. Click on the link to see more images of the heart.

 

 

 

 

 

 

 

 

 

This process does take a while, but there are risk factors that can accelerate the process. To give a more visual understanding of the process there is a video here.

 

Video supplied by Alila Medical media. Click on the link to see other heart videos.

The different exam boards at A level have slightly different approaches as to how the artery deposits build up.

OCR.

A fatty deposit builds up in the wall of the artery. This build up is known as an atheroma and it will narrow the lumen of the arteries. As the lumen of the artery becomes narrower it will be harder for the blood to be pumped through by the heart. This will put strain on the heart, making it work harder increasing the blood pressure. The high blood pressure can damage the endothelium of the artery. This can cause a clot to form (Thrombus, see image below). The clot can break off and wedge in the atheroma blocking the artery completely. If this blocks the coronary arteries around the heart it will cause a heart attack. In addition as the atheroma forms the artery walls will harden and this is known as arteriosclerosis. This is caused by minerals being deposited in the artery wall.

AQA

Again an atheroma forms by streaks form within the wall of the artery. This is normally caused by white blood cells taking up low density lipoproteins (LDLs). Eventually, a atheromatous plaque forms which reduces the size of the lumen. As a result less blood will flow through the artery. There are normally two developments that can occur. Either a thrombus will result or a aneurysm. A thrombus (see image below) is when the atheroma breaks through the endothelium lining. See the video above for the details of this. This will cause blood clotting due to the rough surface. Under normal circumstances the endothelium is designed to be smooth to reduce friction. The clot that forms can actually block the vessel. Again this is illustrated by the video above. If this occurs in the coronary arteries that supply the heart muscle it can lead to a heart attack. An aneurysm is where the artery walls become weakened. A balloon type structure forms which can burst. If this bursts it will cause internal bleeding, lowering the persons blood pressure. Strokes are sometimes caused by a brain aneurysm bursting. See the diagram of an aneurysm below: Aneurysm

 

 

 

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Diagram of a Thrombus.

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Image supplied by Alila Medical media. Click on the link to see other images of the heart and circulatory system. This image shows how a thrombus is formed from blood cells, fibrin and platlets.

Heart attack (myocardial infarction)

A heart attack as the blood supply to the heart muscle will be reduced or stopped. The heart cells will not receive oxygen and so they will respire anaerobically as they will not be able to use aerobic respiration. However, this will not release enough energy for them to survive. As a result they will die. The video below shows the stages of a heart attack

Video supplied by Alila Medical media. Click on the link to see other heart videos.