Transport in Humans
Structures and Functions in Living Organisms · 6 question types
Exam Frequency Analysis
Past paper frequency (2018 to 2024)
This topic accounts for approximately 15% of your exam marks.
The heart, blood vessels, and blood components are regularly tested, particularly structure-function links.
Coronary heart disease (CHD) is the leading cause of death in many developed countries. It develops when the coronary arteries (the small arteries that supply the heart muscle itself) become narrowed by fatty deposits.
How it develops
- Cholesterol and other lipids in the blood get deposited on the inside walls of the coronary arteries, forming patches called atheromas (sometimes called fatty plaques).
- The atheromas gradually narrow the lumen of the artery, restricting the flow of blood to the heart muscle.
- The rough surface of an atheroma can trigger a blood clot to form. The clot blocks the artery further, or even completely.
Two outcomes
- Partial blockage: the heart muscle still gets some blood but not enough during exercise. This causes a sharp, gripping chest pain called angina, especially during physical exertion.
- Complete blockage: the patch of heart muscle fed by that artery is suddenly cut off from oxygen. Cells in that region cannot respire aerobically and quickly die. This is a heart attack (medically, a myocardial infarction). If a large enough area dies, or if the dying area includes the heart's electrical pacemaker, the heart may stop beating altogether.
Risk factors
Coronary heart disease has several risk factors that increase a person's chance of developing it. Most can be managed, given the right lifestyle choices:
| Risk factor | Why it raises the risk |
|---|---|
| High-fat diet (especially saturated fat and cholesterol) | Raises blood cholesterol, accelerating atheroma formation |
| High blood pressure (hypertension) | Increased force damages the artery walls, making it easier for atheromas to form |
| Smoking | Nicotine raises blood pressure; carbon monoxide reduces blood oxygen capacity; chemicals damage artery walls |
| Obesity | Strains the heart, raises blood pressure, often goes with high-fat diet and low activity |
| Lack of exercise | A weaker heart pumps less efficiently; exercise normally helps maintain healthy blood vessels |
| Type 2 diabetes | High blood glucose damages artery walls over time |
| Age | Atheromas slowly accumulate over a lifetime |
| Family history (genetics) | Some people inherit higher blood cholesterol or higher blood pressure |
| Sex | Men are at higher risk than premenopausal women |
| Stress | Raises blood pressure long-term |
The first six are within the patient's control. Stopping smoking, eating less saturated fat, exercising more, losing weight and keeping diabetes under control all reduce CHD risk substantially.