BI100 Lecture 19.1

Arteriosclerosis

• A general term for the hardening and thickening of arteries.

• Arterio means Artery, Sclerosis/Sclerotic means hardening.

• Hardening of the artery walls.

• Characterized by loss of elasticity, reduced ability to expand and contract, and potential calcium buildup.

• Can affect arteries throughout the body.

Atherosclerosis

• A specific type of arteriosclerosis.

• Hardening of the artery due to the accumulation of fatty deposits (plaques).

• Fatty deposits, primarily composed of LDL (low-density lipoproteins), form an atheroma (plaque) on the endothelium (inner lining of blood vessels).

• The plaque can restrict blood flow, leading to ischemia and potential tissue damage.

• Epidemic in economically developed societies due to dietary habits and lifestyle.

• Risk factors include age, gender, genetics, smoking, tobacco use, obesity, hypertension, elevated blood cholesterol, diabetes, and a sedentary lifestyle.

• Most common sites:

  • Aorta: Blockage can lead to aortic aneurysms (bulging of the aorta) and problems throughout the upper and lower body, potentially affecting major organs.

  • Coronary artery: Blockage can lead to myocardial infarct (heart attack), causing damage to the heart muscle due to lack of oxygen.

  • Cerebral artery: Blockage can lead to cerebral infarct (stroke), resulting in brain damage and neurological deficits.

• Infarct: Deadened tissue resulting from a lack of blood supply (ischemia).

Progression of Atherosclerosis

1. Normal Artery

• Three layers:

  • Endothelium (inner lining): A single layer of cells that provides a smooth surface for blood flow.

  • Smooth muscle, elastic fiber: Allows the artery to expand and contract with each heartbeat.

  • Connective tissue: Provides structural support and anchors the artery to surrounding tissues.

• Lumen (space for blood flow) is full and unobstructed.

2. Damaged Artery

• Damage to the endothelium can be caused by:

  • Bacteria: Infections can inflame and damage the endothelium.

  • Nicotine (smoking): Chemicals in tobacco smoke are toxic to the endothelium.

  • Hyperlipidemia (high lipids in the blood): High levels of LDL cholesterol can accumulate in the artery wall.

  • Hypertension (high blood pressure): High pressure can physically damage the endothelium.

  • Other factors: Diabetes, inflammation, and genetic predisposition.

3. Injured Endothelium

• Cholesterol (largely due to high LDL) begins to collect in the damaged area.

• Multiplication of white blood cells (containing lipid) and smooth muscle cells occurs in response to the injury.

• Formation of a fibrous plaque (atheroma): A buildup of cholesterol, cells, and other substances, making the lumen smaller and restricting blood flow.

4. Plaque Formation and Clotting

• Platelets accumulate at the site of the plaque, leading to blood clotting.

• Formation of a thrombus (clot): A blood clot that forms within the artery.

• Fibrin (a protein) accumulates, further stabilizing the clot.

5. Calcification

• More lipids accumulate within the plaque, and calcium deposits (calcification) occur, hardening the plaque.

• Calcification leads to hardening of the artery wall (arteriosclerosis), making it less flexible.

6. Blockage and Ischemia

• Eventually, the artery can become completely blocked by the plaque and clot.

• Insufficient blood flow (ischemia) results in tissues downstream of the blockage.

• If blood flow is not restored quickly, tissue death (infarct) occurs due to oxygen deprivation.

7. Consequences of Atherosclerosis

• Decreased blood flow to the heart, brain, and other tissues, leading to various health problems.

• Arteries lose elasticity, making it harder for them to expand and contract, which increases blood pressure.

• The heart has to work harder to pump blood through the narrowed arteries, which can lead to high blood pressure and heart failure.

• A clot can dislodge and block another artery (throwing a clot), leading to a stroke or heart attack.

Coronary Artery Disease

• A specific type of atherosclerosis that affects the coronary arteries, which supply blood to the heart muscle.

• Gives rise to angina pectoris (chest pain) and myocardial infarct (heart attack).

• Myocardial infarct: Death of part of the heart muscle due to prolonged ischemia.

Angina Pectoris

• Chest pain due to decreased blood flow to the heart (partial blockage of a coronary artery).

• Leads to decreased oxygenation of the heart muscle (ischemia).

• Symptoms: Gripping, vice-like pain and pressure, particularly on the left arm, left shoulder, back, and chest, often triggered by exertion or stress.

Myocardial Infarct (Heart Attack)

• Usually results from a complete and prolonged blockage of the coronary artery, leading to a critical lack of oxygen to the heart muscle.

• Infarct: Death of tissue due to prolonged ischemia.

• The dying portion of the heart develops altered electrical impulses, upsetting the heartbeat (arrhythmia).

• Arrhythmia can lead to fibrillation (wild, uncoordinated twitching of the heart muscle), which prevents the heart from pumping blood effectively.

• If heart muscle dies, it is not replaced by functional tissue, so the heart is permanently weakened, potentially leading to heart failure.

Symptoms of a Heart Attack

• Pressure and squeezing sensation in the chest, often described as an elephant sitting on the chest.

• Sweating, often cold and clammy.

• Shortness of breath, difficulty breathing.

• General nausea, vomiting.

• Lightheadedness or dizziness.

• Two-thirds of heart attack victims die within minutes or hours of the attack, often due to arrhythmia.

• If the heart continues to beat erratically (ventricular fibrillation), a defibrillator can be used to send an electrical shock to restore the normal beat. A defibrillator removes the fibrillation by depolarizing all the heart cells simultaneously.

• If the heart stops beating (cardiac arrest), death occurs in about 4-6 minutes due to lack of oxygen to the brain.

• The damaged heart is permanently weakened, increasing the risk of future heart problems and heart failure.