BTEC Applied Science Unit 1 Biology - The Science Behind Atherosclerosis

Atherosclerosis cause heart disease

Atherosclerosis is a condition that affects the arteries and is a major cause of cardiovascular diseases such as coronary heart disease, stroke, and heart attack. To understand atherosclerosis properly for BTEC Unit 1, students must first understand the role of endothelial tissue in blood vessels.

What Is Endothelial Tissue?

Endothelial tissue forms a thin layer of squamous epithelial cells that line the inside of blood vessels. These cells form the endothelium.

Endothelium inside blood vessels

Structure:

• One cell thick

• Smooth surface

• Selectively permeable

• Supported by a basement membrane

Function:

• Reduces friction as blood flows

• Controls movement of substances into and out of the bloodstream

• Releases chemicals that regulate blood vessel dilation

• Prevents unnecessary blood clotting

A healthy endothelium is essential for maintaining normal blood flow.

What Is Atherosclerosis?

Atherosclerosis is the build-up of fatty plaques inside arteries. These plaques narrow the artery, restrict blood flow, and can lead to clot formation.

It begins with damage to endothelial cells.

Step-by-Step Development of Atherosclerosis

1. Endothelial Damage

Risk factors such as:

• High blood pressure

• Smoking

• High LDL cholesterol

• Diabetes

• Obesity

All these can damage the endothelial lining. When damaged, the endothelium becomes:

• Less smooth

• More permeable

• More likely to trigger inflammation

2. LDL Cholesterol Enters the Artery Wall

Low-density lipoprotein (LDL), often called “bad cholesterol”, can enter the artery wall through the damaged endothelium. Inside the wall, LDL becomes oxidised.

Lipid collection in blood vessel walls

3. Inflammatory Response

The immune system detects oxidised LDL as a threat.

• White blood cells (macrophages) move into the artery wall

• They engulf oxidised LDL

• These become foam cells

Foam cells accumulate and form fatty streaks.

4. Plaque Formation

Over time:

• Smooth muscle cells multiply

• A fibrous cap forms over the fatty deposit

• Calcium may accumulate

This creates a plaque. The artery becomes:

• Narrower

• Less elastic

• More prone to blockage

Plaque formation

5. Risk of Blood Clots

If the fibrous cap ruptures:

• Platelets stick to the damaged area

• A clot (thrombus) forms

• Blood flow may be partially or completely blocked

This can cause:

• Heart attack (coronary artery blockage)

• Stroke (cerebral artery blockage)

Linking - Endothelial Tissue and Risk Factors

You need to understand how risk factors damage endothelial cells.

Smoking

• Chemicals in cigarette smoke damage endothelial cells

• Increases inflammation

• Reduces oxygen delivery

High Blood Pressure

• Increased force damages vessel lining

• Makes endothelial surface rough

High LDL Cholesterol

• Increases likelihood of lipid accumulation

• Promotes plaque development

Smoking is a risk factor

Diabetes

• High blood glucose damages endothelial cells

• Increases oxidative stress

Why the Endothelium Is So Important

The endothelium normally:

• Produces nitric oxide (NO), which dilates blood vessels

• Prevents clot formation

• Maintains smooth blood flow

When damaged:

• Nitric oxide production decreases

• Vessels constrict

• Clotting risk increases

• Inflammation is triggered

This loss of function is central to atherosclerosis.

Exam-Ready Summary (6–8 Mark Answer Style)

Atherosclerosis begins with damage to the endothelial lining of arteries. Risk factors such as high blood pressure, smoking and high LDL cholesterol damage endothelial cells, making them more permeable. LDL cholesterol enters the artery wall and becomes oxidised, triggering an inflammatory response. Macrophages engulf the oxidised LDL to form foam cells, which accumulate and form fatty streaks. Smooth muscle cells then proliferate and form a fibrous cap, creating a plaque that narrows the artery. If the plaque ruptures, a blood clot may form, potentially leading to a heart attack or stroke.

Key Terms to Remember

• Endothelium

• LDL cholesterol

• Oxidation

• Foam cells

• Plaque

• Thrombus

• Nitric oxide

• Inflammation

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