By the end of this lesson
- Explain smoking damage to airways and alveoli.
- Explain effects on oxygen transport and circulation.
- Link smoking mechanisms to coronary heart disease risk.
BIG QUESTION
How can inhaled smoke increase the risk of disease in organs far beyond the lungs?
Smoke damages respiratory defences and exchange surfaces while nicotine, carbon monoxide and vascular injury affect the circulatory system.
Smoke weakens airway defence
Tobacco smoke irritates airway lining, increases mucus production and damages or paralyses cilia. Mucus and pathogens accumulate, increasing infection risk and contributing to chronic bronchitisLong-term inflammation of the bronchi, often caused by smoking, with excess mucus and a persistent cough..
Persistent inflammation narrows airways and increases resistance to airflow.
Emphysema destroys exchange structure
Long-term inflammation recruits cells and enzymes that damage alveolar walls and elastic fibres. Adjacent air spaces merge and recoil is reduced.
emphysemaA lung disease, often caused by smoking, in which the walls of the alveoli break down, reducing the surface area for gas exchange. therefore reduces exchange area and makes exhalation difficult, causing breathlessness. It is not simply tar coating otherwise intact alveoli.
Carcinogens increase cancer risk
Smoke contains carcinogens that damage DNA. Mutations affecting cell-cycle control can allow uncontrolled division and tumour formation.
Risk increases with exposure but is probabilistic: smoking greatly raises risk without making disease inevitable in every individual.
Carbon monoxide reduces oxygen transport
carbon monoxideA poisonous gas in cigarette smoke that binds to haemoglobin more strongly than oxygen, reducing the oxygen the blood can carry. binds haemoglobin with much greater affinity than oxygen, forming carboxyhaemoglobin and reducing oxygen-carrying capacity. Binding is strong but not literally irreversible.
Tissues may receive less oxygen, increasing strain on the cardiovascular system.
Smoking raises coronary heart disease risk
Nicotine stimulates heart rate and can constrict blood vessels. Smoke exposure damages vessel lining, promotes inflammation and increases clotting tendency.
Atherosclerotic plaque and thrombosis can narrow or block coronary arteries, reducing oxygen supply to heart muscle and causing angina or myocardial infarction.
Smoke component to consequence
High-quality answers use a causal chain rather than a list of diseases.
| Exposure/effect | Immediate biological change | Possible consequence |
|---|---|---|
| Irritants and particulates | Cilia damaged; mucus increases. | Bronchitis and infection. |
| Inflammation/protease activity | Alveolar walls and elastin damaged. | Emphysema and reduced gas exchange. |
| Carcinogens | DNA mutations accumulate. | Lung and other cancers. |
| Carbon monoxide | Haemoglobin oxygen carriage falls. | Reduced tissue oxygenation. |
| Nicotine/vascular injury | Heart rate, vasoconstriction, clot/plaque risk increase. | Coronary heart disease and stroke risk. |
Language that earns precision
- chronic bronchitis
- Long-term airway inflammation with excessive mucus and persistent cough.
- emphysema
- Destruction of alveolar walls and elastic recoil, reducing gas-exchange area.
- carcinogen
- An agent that increases cancer risk by causing or promoting cellular damage.
- carboxyhaemoglobin
- Haemoglobin bound to carbon monoxide.
- coronary heart disease
- Disease caused by impaired blood supply through coronary arteries.
Common misconceptions
Claim: Tar merely blocks alveoli like plugs.
Correction: Smoke drives inflammation and tissue destruction; emphysema involves loss of alveolar walls and elasticity.
Claim: Carbon monoxide binds haemoglobin irreversibly.
Correction: Its affinity is very high, but binding can reverse after exposure stops.
Claim: Nicotine is the main carcinogen in smoke.
Correction: Nicotine drives dependence and cardiovascular effects; many other smoke chemicals are carcinogenic.
Claim: Smoking causes coronary disease only because lungs absorb less oxygen.
Correction: It also damages vessels, promotes plaques and clotting, and changes cardiovascular activity.
Match the answer to the command word
Use exposure → cellular/tissue damage → organ effect → disease risk.
Keep bronchitis, emphysema, cancer and coronary disease mechanisms separate.
Say smoking increases probability; avoid claiming every smoker develops the same disease.
Recall, apply, then justify
Explain how smoking can cause emphysema and breathlessness.
Hint
Inflammation → wall damage → area/recoil.
Suggested marking points
- Smoke causes chronic inflammation in lung tissue.
- Enzymes/cells damage alveolar walls and elastic fibres.
- Surface area and elastic recoil decrease.
- Gas exchange and exhalation become less effective, causing breathlessness.
Explain how carbon monoxide affects oxygen transport.
Hint
Name the molecule it binds.
Suggested marking points
- Carbon monoxide binds strongly to haemoglobin.
- Less haemoglobin is available to carry oxygen.
- Blood oxygen-carrying capacity and tissue oxygen delivery fall.
Explain two mechanisms linking smoking to coronary heart disease.
Hint
Use vessels/clots and cardiac demand.
Suggested marking points
- Smoke damages vessel lining and promotes atherosclerosis or clot formation.
- This can narrow/block coronary arteries.
- Nicotine increases heart rate/vasoconstriction.
- Cardiac oxygen demand rises while supply may be reduced.
Evaluate why an observational study showing more heart disease among smokers supports but cannot alone prove a simple one-factor cause.
Planning hint
Use mechanism, dose response and confounding.
What a strong design includes
- A strong association is consistent with biological mechanisms.
- Dose–response and reduced risk after quitting strengthen causal inference.
- Random assignment to smoking would be unethical.
- Diet, occupation, deprivation and other exposures can confound observational data.
- Measurement of smoking exposure may be inaccurate.
- Converging epidemiological and mechanistic evidence supports causation despite no single perfect study.