IB Biology Topic B3.2.6: Causes and Consequences of Occlusion of the Coronary Arteries Notes

The Coronary Arteries Supply Oxygen to the Heart Muscle

1. The coronary arteries deliver oxygen-rich blood to the heart's muscular walls, the myocardium.
2. The heart contracts non-stop, so it needs a constant supply of oxygen and nutrients to keep pumping.
3. Right coronary artery: supplies the right side of the heart.
4. Left coronary artery: divides into the left anterior descending and circumflex arteries, supplying the left side of the heart.

Atherosclerosis: How Coronary Arteries Become Blocked

1. Coronary heart disease (CHD) occurs when the coronary arteries become narrowed or blocked, usually by atherosclerosis.
2. Atherosclerosis develops in stages:
   1. Lipid deposition: saturated fats and cholesterol build up in the arterial walls, forming fatty streaks that grow into plaques.
   2. Calcium impregnation: over time the plaques harden with calcium, reducing flexibility and narrowing the lumen.
3. Several risk factors speed up atherosclerosis:
   1. Hypertension: high blood pressure damages arterial walls, making plaque more likely.
   2. Smoking: nicotine causes vasoconstriction, raising blood pressure and promoting plaque buildup.
   3. Obesity and poor diet: diets high in saturated fats, sugar, and salt raise cholesterol and blood pressure.
   4. Sedentary lifestyle: lack of activity weakens cardiovascular health and worsens obesity.
   5. Genetic factors: some people inherit a tendency toward high cholesterol or hypertension.
   6. Diabetes: poorly controlled blood sugar increases the risk of atherosclerosis.

Consequences: From Chest Pain to Heart Failure

What happens depends on how severely and how long the artery is blocked.

1. Angina (chest pain)
   1. Partial blockage reduces blood flow to the heart, causing chest pain during exertion or stress.
   2. Angina is a warning sign of CHD but does not cause permanent heart damage.
2. Heart attack (myocardial infarction)
   1. A complete blockage, often from a clot on a ruptured plaque, cuts off blood supply entirely.
   2. The heart muscle is starved of oxygen, causing tissue death.
   3. This can be fatal if not treated quickly.
3. Heart failure
   1. If enough heart muscle is damaged, the heart can no longer pump blood well enough to meet the body's needs.
4. Arrhythmias
   1. Damaged heart tissue can disrupt the heart's electrical system, causing irregular rhythms such as ventricular fibrillation.

Reducing the Risk of Coronary Artery Occlusion

1. Diet: emphasise fruits, vegetables, whole grains, and lean proteins, and limit saturated fats, salt, and sugar.
2. Exercise: regular aerobic activity like walking, cycling, or swimming strengthens cardiovascular health.
3. Smoking cessation: quitting reduces vasoconstriction and slows plaque formation.