Atherosclerosis, clotting and cardiovascular risk

What you’ll learn

• Explain the progression from endothelial dysfunction to plaque and thrombosis.
• Distinguish the functions of LDL and HDL particles.
• Evaluate the intended effects and risks of cardiovascular treatments.

Understand the idea

Damage or dysfunction of an artery’s endothelium can promote an inflammatory response and retention of lipids in the wall. Immune cells take up lipid, and a plaque develops beneath the lining. The artery may narrow and become less elastic, restricting flow and contributing to raised pressure. If a plaque ruptures, clotting can produce a thrombus that suddenly obstructs blood supply. A blocked coronary artery can deprive cardiac muscle of oxygen and cause a myocardial infarction.

Clotting normally limits blood loss. In the simplified pathway, damaged tissue and activated platelets initiate events described as thromboplastin release; prothrombin is converted to thrombin, which converts soluble fibrinogen into insoluble fibrin. Fibrin forms a mesh that traps cells. LDL particles deliver cholesterol to tissues, whereas HDL participates in returning cholesterol to the liver. Cholesterol has normal cellular roles, but elevated LDL cholesterol contributes causally to atherosclerosis. An association between high HDL and lower risk does not by itself prove that any intervention raising HDL will be protective.

Risk reflects interacting factors, including inherited susceptibility, age, sex, smoking, inactivity, diet and raised blood pressure. Antihypertensives reduce blood pressure; statins reduce cholesterol synthesis and usually lower LDL; anticoagulants reduce coagulation and platelet inhibitors reduce platelet aggregation. Benefits depend on the individual clinical context and must be weighed against adverse effects, including bleeding with clot-reducing medicines. This is the biology of treatment categories, not a rule for choosing or changing a medicine.

Key formulae

$$\text{prothrombin}\longrightarrow\text{thrombin}$$

$$\text{fibrinogen}\xrightarrow{\text{thrombin}}\text{fibrin}$$

Worked example

An artery contains a plaque. After the plaque surface ruptures, blood flow falls abruptly. Explain why the sudden change is more consistent with thrombosis than with slow plaque growth alone.

1. Plaque growth can narrow the lumen progressively over time.
2. Rupture exposes material that promotes platelet activation and the clotting cascade.
3. A fibrin-containing thrombus can quickly obstruct the remaining lumen, sharply reducing oxygen delivery downstream.

Answer: The rupture can trigger a rapidly forming thrombus on top of the pre-existing plaque.