The Circulatory System

The heart, cardiac cycle, cardiac output, Cardiovascular disease

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The Circulatory System

The circulatory system consists of the heart and blood vessels.
The heart consists of two muscular pumps:

  • The right side pumps deoxygenated blood to the lungs
  • The left side pumps oxygenated blood around the body to the cells.
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The Heart is Adapted to its Job


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The Cardiac Muscle is Myogenic


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Cardiac Cycle


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Cardiac Output Equation

Cardiac output is the volume of blood pumped per minute (cm3 min-1)
Heart rate is the number of heart beats per minute (min-1)
Stroke volume is the volume of blood pumped in each heart beat (cm3)

Cardiac output = Stroke volume x Heart rate 



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Cardiovascular Disease

Often, cardiovascular diseases start with the formation of an atheroma.

An atheroma is a hardened build up of white blood cells, lipids and connective tissue forming a fibrous plaque inside an artery. These build ups can be caused fats and white blood cells clumping under and around damaged areas in the smooth endothelium layer in the artery, which are often caused by high blood pressure.

The plaque can partially block the lumen of an artery which results in the blood flow being restricted, increasing the blood pressure.

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Atheromas Increase the Risk of Aneurysm and Thromb

An aneurysm is a balloon-like swelling in the artery.

  • It is caused an atheroma formation in the artery, which increases the blood pressure.
  • The high blood pressure can weaken the artery, and the blood may push the inner layers of the artery through the outer elastic layer, forming a swelling (aneurysm)
  • If it bursts, it could cause a haemorrhage.

Thrombosis is the formation of a blood clot.

  • An atheroma damages or ruptures the smooth inner layer of the artery, making it have a rough surface.
  • This rough surface can accumulate plateletes and fibrin, forming a clot that can partially or completely block an artery.
  • This blockage can move and block another blood vessel.
  • It can leave debris which can form another clot. 
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A Blood Clot can cause a Myocardial Infarction

The coronary arteries supply the heart muscle with blood, which contains oxygen needed by the heart muscle cells for respiration.

  • If a coronary artery gets completely blocked, that area of the heart will recieve no oxygen from the blood.
  • This could cause a myocardial infarction (heart attack) which can damage or kill the heart muscle. If the blockage is more widespread, it can cause heart failure-which can be fatal.
  • Symptoms- Pain in chest and upper body, shortness of breath and sweating.
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Coronary Heart Disease (CHD)

CHD is when the coronary arteries have a lot of atheromas in them, it is known as a cardiovascular disease.

The risk of CHD can be increased by:

High blood cholesterol and poor diet

  • A high level of blood cholesterol means there is a lot of cholesterol in the blood. Cholesterol is one of the main constituents of the fatty deposits that can cause an atheroma, which could potentially block blood flow to the coronary arteries.
  • A poor diet high in saturated fat can increase blood cholesterol levels. Diets high in salt can also increase blood pressure which increases the chance of damage to the artery walls, increasing the risk of CHD. Being overweight and not exercising can also increase this.
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  • Ciggarette smoke can contain carbon monoxide and nicotine. CO combines with haemoglobin and reduces its oxygen affinity, reducing the amount of oxygen than can be transported round the body. If the heart doesn't get enough oxygen it can lead to a myocardial infarction.
  • Smoking can reduce the amount of antioxidants in the blood, which protect cells from damage. The reduced level of antioxidants means cell damage in the coronary artery walls and an atheroma is more likely.

You can control a lot of factors contributing to CHD, but some people have an uncontrollable genetic predisposition or a condition which increases the risk of CHD.

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