What you need to know
- 1.10Endothelial dysfunction, inflammationA local response to infection or damage: histamine makes blood vessels dilate and become leakier, causing heat, redness and swelling and bringing in phagocytes., plaque formation and raised blood pressureThe pressure that blood exerts on the walls of the blood vessels. in atherosclerosisThe hardening and narrowing of arteries caused by atheromas building up in their walls..
- 1.11thromboplastinA protein released by platelets and damaged tissue. It triggers the conversion of prothrombin into thrombin., prothrombin, thrombinThe enzyme that converts soluble fibrinogen into insoluble fibrin. It is formed from prothrombin., fibrinogenA soluble protein in blood plasma that thrombin converts into fibrin. and fibrinInsoluble protein threads that form a mesh, trapping blood cells to make a clot., and the role of clotting in CVD.
Risk-factor studies, prevention and treatment comparisons belong in section 1C. Here the focus is the mechanism of plaque development and clot formation.
By the end, you should be able to…
- Explain the sequence leading to an atherosclerotic plaque.
- Describe the specified clotting pathway using the correct substances.
- Link a plaque or thrombusA blood clot that forms inside a blood vessel. to reduced tissue oxygen supply.
Build your understanding
A change in the artery wall
The endotheliumThe single layer of flat cells that lines the inside of blood vessels and the heart. is the cell layer lining a blood vessel. Endothelial dysfunction changes its normal protective behaviour and can allow lipid accumulation and inflammatory-cell entry into the arteryA vessel that carries blood away from the heart at high pressure. It has a thick wall with elastic fibres and smooth muscle. wall. It need not begin as a visible tear.
LDLLow-density lipoprotein. It carries cholesterol from the liver to the tissues. High LDL is linked to atheroma. particles enter and are retained in the wall, where they can be modified. Monocytes enter the tissue and become macrophages. These take up lipid and can become foam cells. Lipid and cells accumulate; smooth muscle and fibrous material contribute to a plaque with a lipid-rich region and a fibrous cap. That wall deposit is an atheromaA fatty plaque of cholesterol, white blood cells and fibrous tissue that builds up under the endothelium of an artery.. atherosclerosisThe hardening and narrowing of arteries caused by atheromas building up in their walls. is this process in the artery wall, not simply fat floating in the blood and sticking inside a pipe.
Narrowing, stiffness and pressure
A growing plaque can narrow the lumenThe space inside a tube, such as a blood vessel. and increase resistance to blood flow. Changes to the wall can also reduce its elasticity. These changes can contribute to raised arterial pressure, while raised pressure can worsen endothelial dysfunction: the relationship can reinforce itself.
A narrower lumen does not mean every nearby pressure measurement must increase. The pressure difference across a narrowed region and the wider circulation matter. For this specification, connect increased resistance and reduced elasticity with the tendency towards raised pressure and impaired tissue supply.
The clotting sequence
Clotting normally limits blood loss when a vessel is damaged. plateletA cell fragment in the blood. At a damaged vessel wall, platelets stick together and release thromboplastin. adhere at the affected site, become activated and aggregate. In the simplified specification pathway, damaged tissues and activated platelets lead to thromboplastinA protein released by platelets and damaged tissue. It triggers the conversion of prothrombin into thrombin. activity, initiating a cascade that converts prothrombin into thrombinThe enzyme that converts soluble fibrinogen into insoluble fibrin. It is formed from prothrombin..
Thrombin is an enzymeA globular protein that acts as a biological catalyst, speeding up a specific reaction. that converts soluble fibrinogenA soluble protein in blood plasma that thrombin converts into fibrin. into insoluble fibrinInsoluble protein threads that form a mesh, trapping blood cells to make a clot.. Fibrin forms a mesh that traps blood cells and stabilises the platelet plug. Calcium ions and other clotting factors take part in the cascade, but do not replace the named conversions required here.
Keep the two stages distinct: prothrombin → thrombin; fibrinogen → fibrin. Thromboplastin does not directly turn fibrinogen into fibrin.
When a protective process becomes harmful
If an atherosclerotic plaque ruptures, material exposed to the blood can activate platelets and clotting. A thrombusA blood clot that forms inside a blood vessel. can form at the site and partly or completely block the artery. A clot or fragment that travels through the circulation is an embolusA blood clot, or part of one, that breaks away and is carried in the blood until it blocks a smaller vessel. and may obstruct a narrower vessel elsewhere.
Blockage of a coronary artery reduces oxygen delivery to part of the heart muscle. A severe, sustained interruption can cause death of that tissue: a myocardial infarction, or heart attack. Similar interruption of a brain artery can cause an ischaemic stroke. A plaque and a thrombus are different structures, although a plaque can trigger thrombus formation.
The seriousness of an event depends on more than how narrow the artery was beforehand. A plaque that ruptures can trigger a sudden obstruction; gradual narrowing and acute clotting are related but distinct processes.
Key terms
An atheromaA fatty plaque of cholesterol, white blood cells and fibrous tissue that builds up under the endothelium of an artery. is the plaque in the arteryA vessel that carries blood away from the heart at high pressure. It has a thick wall with elastic fibres and smooth muscle. wall. A thrombusA blood clot that forms inside a blood vessel. is a clot formed in a vessel from plateletA cell fragment in the blood. At a damaged vessel wall, platelets stick together and release thromboplastin. and fibrinInsoluble protein threads that form a mesh, trapping blood cells to make a clot.. An embolusA blood clot, or part of one, that breaks away and is carried in the blood until it blocks a smaller vessel. is a clot or fragment that has left its formation site and may block a narrower vessel. The biological order can loop: endothelial dysfunction → atheroma → narrower, stiffer artery → higher pressure → more endothelial stress. Rupture is a branch, not the next compulsory step: atheroma rupture → thrombus → reduced oxygen supply.
You may write the answer starting from the heart attack and work backwards, as long as each “because” is a mechanism. Equal lumenThe space inside a tube, such as a blood vessel. size does not mean equal immediate risk if only one atheroma has ruptured.
Diagram A
NOT: an atheroma is the wall plaque. A thrombus is the clot in the lumen.
- Narrowing raises resistance; elasticity can fall
- Raised pressure and endothelial damage can reinforce each other
- An embolus is a clot or fragment that has travelled
- A blocked coronary artery can cause a myocardial infarction
Two traps this diagram blocks
- Do not call the plaque a blood clot. The clot is the thrombus that may form after rupture.
- Equal narrowing does not mean equal immediate risk. Only the ruptured plaque has triggered clotting.
From the diagram alone
Question
Explain how a ruptured coronary atheroma can cause a myocardial infarction. [4]
Show a model answer
Rupture exposes material that activates platelets and the clotting cascade. A thrombus can form and block the coronary artery. Heart muscle supplied by that artery no longer receives enough oxygen for aerobic respiration. If the interruption is severe and sustained, those cells die.
Diagram B
NOT: thromboplastin does not directly turn fibrinogen into fibrin.
- Two conversions: prothrombin → thrombin; fibrinogen → fibrin
- Thrombin is the enzyme. Fibrinogen is the substrate
- A protective clot can become a harmful thrombus
- Calcium ions take part, but do not replace these names
Two traps this diagram blocks
- Do not swap the endings: thrombin is the enzyme; fibrin is the insoluble fibre.
- Do not say the blood has been “thinned”. Name the conversion that has been reduced.
From the diagram alone
Question
Describe the pathway from thromboplastin activity to a fibrin mesh. [4]
Show a model answer
Thromboplastin activity starts a cascade that converts prothrombin to thrombin. Thrombin then converts soluble fibrinogen to insoluble fibrin. Fibrin fibres form a mesh that traps blood cells and stabilises the platelet plug.
| Starting substance | Change | Result |
|---|---|---|
| Prothrombin | Activated through a cascade initiated by thromboplastin activity | Thrombin: an enzyme |
| Fibrinogen: soluble | Converted by thrombin | Fibrin: insoluble fibres forming a mesh |
Make your reasoning visible
Build the explanation
X happens because Y, leading to Z. X: heart muscle dies. Y: a ruptured coronary atheromaA fatty plaque of cholesterol, white blood cells and fibrous tissue that builds up under the endothelium of an artery. triggers a thrombusA blood clot that forms inside a blood vessel. that blocks the arteryA vessel that carries blood away from the heart at high pressure. It has a thick wall with elastic fibres and smooth muscle.. Z: that region can no longer receive enough oxygen for aerobic respiration. Incomplete: “Fat clogs the artery and causes a heart attack.” Improved: “A ruptured atheroma exposes material that activates clotting, so a thrombus can block the coronary artery and starve heart muscle of oxygen.” The improvement separates the wall deposit from the clot.
Name the enzyme and its substrate
thrombinThe enzyme that converts soluble fibrinogen into insoluble fibrin. It is formed from prothrombin. acts on fibrinogenA soluble protein in blood plasma that thrombin converts into fibrin. to form fibrinInsoluble protein threads that form a mesh, trapping blood cells to make a clot.. “A clot forms” misses the specified molecular steps. Check the endings of these similar names before finishing.
Explain the link to tissue damage
A blocked coronary artery reduces oxygen supply to heart muscle, limiting aerobic respiration; a prolonged severe interruption can kill cells. Do not say that the heart chambers simply stop containing blood.
Avoid this misconception
The claim: A plaque is the same thing as a blood clot.
The correction: A plaque develops in the artery wall and contains lipid, cells and fibrous material. A thrombus forms from plateletA cell fragment in the blood. At a damaged vessel wall, platelets stick together and release thromboplastin. and the clotting process within a vessel; plaque rupture can trigger it.
Put the clotting cascade in order
Clotting is a cascade: each step makes the next one happen. Order the named conversions, then try the chain that leads from a damaged artery wall to a plaque.
Order the steps
What to do
- Pick a chain with Chain, just below these steps: Clotting or Atherosclerosis.
- Reorder the cards below: drag a card (on a touch screen, drag its number), tap a card then tap where it goes, or use the ↑ and ↓ arrows at its right.
- Press Check under the cards to mark each one green (right place) or red; the count shows how many are right.
- Stuck? Hint first outlines the first wrong place, then gives a clue, then places that step for you.
- Shuffle mixes the cards again; Start again returns them to the starting order. Keyboard: Space picks up, arrow keys move, Space drops.
A blood vessel is cut. Put the clotting steps in order, from the damage to the finished clot.
0 of 6 in the right place
Clotting involves many more factors than the ones named here; the specification names thromboplastin, prothrombin, thrombin, fibrinogen and fibrin. Rupture is not inevitable: many plaques narrow an artery for years without one.
Check your understanding
Try each question before opening the suggested answer.
Practice question
Retrieval and explanation · suggested answer
Describe the clotting pathway from thromboplastin activity to formation of a fibrin mesh.
Show suggested answer
Thromboplastin activity initiates a cascade leading to conversion of prothrombin to thrombin. Thrombin converts soluble fibrinogen to insoluble fibrin. Fibrin fibres form a mesh that traps cells and stabilises the platelet plug.
Practice question
Retrieval and explanation · suggested answer
Explain how a ruptured coronary plaque can lead to a myocardial infarction.
Show suggested answer
Rupture exposes material that activates platelets and clotting. A thrombus may block the coronary artery, reducing oxygen supply to heart muscle. If the interruption is severe and sustained, cells die, causing a myocardial infarction.
Take the idea further
Apply the same specification knowledge to an unfamiliar problem. Any extra assumptions are supplied in the question.
Stretch question
Two model plaques cause the same narrowing. Plaque A has an intact cap; plaque B has ruptured and exposed clot-triggering material. Explain why lumen size alone may fail to predict the immediate risk of obstruction.
Show a hint
Consider what can happen after the wall becomes exposed to blood.
Explore the reasoning
The ruptured plaque can activate platelets and the clotting cascade, rapidly adding a thrombus to the existing narrowing. The intact plaque has not undergone that event in the model. Equal initial lumen sizes therefore do not guarantee equal immediate obstruction risk.
Recall this lesson
Lesson recall questions
Question 1 of 5: Explain, in causal order, why a narrowed lumen can raise blood pressure and then worsen the plaque.
Atherosclerosis sequence
Practice question
Retrieval and explanation · suggested answer
Explain, in causal order, why a narrowed lumen can raise blood pressure and then worsen the plaque.
Build the sequence from memory first. Then reveal the model order.
Tap the steps in the order you recall. Tap a placed step to send it back.
- 01Next step
- 02Waiting
- 03Waiting
Tap to place
Put your biology to work
Explore where these ideas appear in the world. Enrichment, not extra required recall.
More than “clogged pipes”
1B · AtherosclerosisResearch and clinical explanations of atherosclerosis include inflammation and cells within the artery wall. The familiar “clogged pipe” image captures narrowing, but leaves out the living tissue and…Specification 1.10 · 1.11Read & use the scienceClose article
Why this matters
Research and clinical explanations of atherosclerosis include inflammation and cells within the artery wall. The familiar “clogged pipe” image captures narrowing, but leaves out the living tissue and biological processes that create a plaque. A plaque is a biological change in an artery wall, involving lipids and cells, rather than loose fat poured into a pipe. A disrupted plaque can promote formation of a thrombus that suddenly restricts supply. The distinction matters because a gradual narrowing and an acute clot need not produce the same timing of symptoms. Connecting wall changes, clotting and oxygen delivery gives a more useful explanation than a cartoon of greasy plumbing, even when that cartoon dominates popular descriptions.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.10 understand the course of events that leads to atherosclerosis (endothelial dysfunction, inflammatory response, plaque formation, raised blood pressure)
- 1.11 understand the blood clotting process (thromboplastin release, conversion of prothrombin to thrombin and fibrinogen to fibrin) and its role in cardiovascular disease (CVD)
Use the science
A video shows cooking fat poured into a drain as its complete explanation of atherosclerosis. Identify one useful feature of the analogy and two important limitations.
Explore a possible response
It illustrates that narrowing can restrict flow. It does not represent inflammatory cells and lipid processing within a living artery wall, or plaque rupture triggering a platelet-and-fibrin thrombus. It also risks implying that dietary fat simply deposits directly as a lump.
Explore the source
Plastic in an artery: discovery or proof?
1B · AtherosclerosisA 2024 observational study analysed plaques removed from people undergoing carotid-artery surgery. Patients whose plaques contained detected plastics had a higher subsequent rate of a combined outcome involving…Specification 1.10 · 1.15 · 1.16Read & use the scienceClose article
Why this matters
A 2024 observational study analysed plaques removed from people undergoing carotid-artery surgery. Patients whose plaques contained detected plastics had a higher subsequent rate of a combined outcome involving heart attack, stroke or death. That finding connects an environmental exposure with the living, inflammatory tissue of an atheroma. It does not demonstrate that the plastics caused those events: the groups may differ in other ways, and these were selected patients with existing artery disease. The important research question is how detection, biological mechanism and clinical outcome fit together. Each requires evidence; none is automatically established by the others.
Back to the specification
Pearson Edexcel IAL Biology · Issue 2, February 2021 · Unit 1, pp. 15–18. The application extends beyond required recall.
- 1.10 understand the course of events that leads to atherosclerosis (endothelial dysfunction, inflammatory response, plaque formation, raised blood pressure)
- 1.15 be able to analyse and interpret quantitative data on illness and mortality rates to determine health risks, including distinguishing between correlation and causation and recognising conflicting evidence
- 1.16 be able to evaluate the design of studies used to determine health risk factors, including sample selection and sample size used to collect data that is both valid and reliable
Use the science
Why would finding plastic and inflammatory markers in the same plaque still be insufficient to establish that plastic caused the inflammation?
Explore a possible response
Co-occurrence does not establish timing or exclude confounding and preferential accumulation in damaged tissue. Controlled mechanistic evidence and additional studies would strengthen inference.
Explore the source
- Microplastics and Nanoplastics in Atheromas and Cardiovascular EventsMarfella et al., New England Journal of Medicine (2024)