AS/A-level Biology - Coronary Heart Disease

• This is a multi-factorial disease.
• It can be caused by a high salt diet and a high fat diet, both lead to the same process - atherosclerosis.
• Myocardial infarction is the loss of sufficient blood flow to a tissue to allow it to carry out its normal activity.
• Severe myocardial infarction may cause the heart to stop beating - cardiac arrest.

When it comes to AS/A-level Biology, do you know how does an artery get damaged?

High Salt Diet

• When salt is consumed, it increases the content of salt in the blood.
• This causes a low water potential inside the blood due to the added salt.
• Osmosis occurs due to the movement of water from a high water potential to a low water potential.
• This leads to an increased volume in the blood due to the movement.
• This will cause a high pressure in the blood because of the high volume, this leads to hypertension - increased pressure inside arteries causing cracks in the blood vessels and damaging the epithelium.

High Saturated and Unsaturated Fats Diet

• Lipoproteins are made in the liver.
• They transport cholesterol as it is not soluble.
• Proteins can be classified into:
  (1) Lots of proteins: high density lipoproteins (HDLs)
  (2) More lipid, less proteins: low density lipoproteins (LDLs).

LDLS

• They take cholesterol and lipids to the tissue from the liver.
• They tend to deposit the cholesterol that they carry into damaged artery walls.
• Diets high in saturated days (red meat, eggs, cheese) may result in high LDL cells.

Do you remember how plaque is formed in AS/A-level Biology?

• The hardening of the arteries) in the coronary arteries.

1. Cholesterol is deposited in the artery walls.
2. Macrophage (type of white blood cell) engulf the LDL.
3. They become enlarged, known as foam cells located in the artery walls; seen as fatty streaks.
4. They are sealed with a fibrous capsule known as plaque.
5. The plaque stretches and the tunica externa expands.
6. The narrowed lumen is caused by an increased plaque and reduced elasticity. This can lead to angina: pains in the heart.
7. Calcium is deposited in the plaque which makes it hard and inflexible.
8. As the plaque grows, there is an even narrower lumen. It is ruptured via the increased pressure due to the narrow lumen. This is known as coronary thrombosis where there is a blood clot on and around the plaque.
9. Platelets clot the fibrous tissues and this blocks the artery.
10. Flow can be stopped and this may cause a stroke (in the brain) or myocardial infarction which can lead to cardiac arrest.

• Smoking
• Diabetes
• High blood pressure
• High cholesterol levels

That's the end of the topic!

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