Smoking, the lungs and the circulatory system

Structure and functions in living organisms · Gas exchange in humans · note 4 of 5

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Smoking, the lungs and the circulatory systemSpec 2.49

In short

Smoking damages the lungs and circulatory system. Tar contains carcinogens that cause lung cancer and destroys cilia, so mucus is not removed. Carbon monoxide combines with haemoglobin, so red blood cells carry less oxygen. Nicotine is addictive and raises heart rate and blood pressure. Smoking also causes chronic bronchitis and emphysema and increases the risk of coronary heart disease.

Tobacco smoke contains many harmful substances. The three you need to know about are tar, carbon monoxide and nicotine.

Harmful substances in tobacco smoke
Substance	Effect
Tar	Contains carcinogens (chemicals that cause cancer), so increases the risk of lung cancer. Also damages the airway lining.
Carbon monoxide	Combines with haemoglobin in red blood cells, so they carry less oxygen. The heart has to work harder to supply the body with oxygen.
Nicotine	An addictive drug. It increases heart rate and blood pressure.

Effects on the lungs

The airways are lined with ciliated cells, which have tiny hairs (cilia), and goblet cells, which make mucus. Mucus traps dust and bacteria, and the cilia sweep it up to the throat.
Tar damages and destroys the cilia, so mucus and the microorganisms in it stay in the airways. This causes infections and a smoker's cough.
Chronic bronchitis: smoke irritates the airways, so goblet cells make more mucus. The airways become inflamed and blocked with mucus, which makes breathing difficult.
Emphysema: the walls of the alveoli break down, so the surface area for gas exchange is much smaller. The person is short of breath.
Lung cancer: carcinogens in tar can make lung cells divide out of control and form a tumour.

Effects on the circulatory system

Smoking raises the risk of coronary heart disease. In this disease the coronary arteries, which supply the heart muscle with oxygenated blood, become narrowed by fatty deposits. Less blood reaches the heart muscle, so it gets less oxygen. If a coronary artery is completely blocked, part of the heart muscle is starved of oxygen and a heart attack results.

Smoking makes this more likely. Chemicals in smoke and raised blood pressure damage the lining of the arteries, so fatty deposits build up more easily and blood clots are more likely to form. Nicotine raises heart rate and blood pressure, and carbon monoxide reduces the oxygen carried by the blood, so the heart has to work harder.

Exam tip:

Name the substance, then state its effect. 'Smoking damages the lungs' gains nothing: say that tar destroys the cilia, so mucus is not removed.

Sections of the airway lining. Healthy: ciliated cells with cilia sweeping a thin layer of mucus containing trapped bacteria up to the throat, and goblet cells. Smoker's: tar on the cells, the cilia destroyed, a thick layer of mucus with many trapped bacteria, and enlarged goblet cells. — Tar destroys the **cilia**, so mucus and the bacteria trapped in it are not removed from the airways.

Written and checked against the Edexcel IGCSE Science Double Award (4SD0) specification · Updated October 2026

Frequently asked questions

How are alveoli adapted for gas exchange?

Alveoli are adapted for gas exchange by diffusion. Millions of alveoli give a very large surface area, and their walls and the capillary walls are each one cell thick, giving a short diffusion distance. A rich capillary network and ventilation maintain a steep concentration gradient, and the moist lining lets gases dissolve.

What happens when you breathe in?

When you breathe in, the intercostal muscles contract and move the ribs up and out, and the diaphragm contracts and flattens. This increases the volume of the thorax, so the pressure inside falls below atmospheric pressure. Air moves from the higher pressure outside into the lungs. The lungs themselves have no muscle.

How does smoking affect the lungs?

Smoking damages the lungs because tar destroys the cilia, so mucus and trapped microorganisms are not removed, causing infections and a smoker's cough. Smoke irritates the airways, causing chronic bronchitis. In emphysema the alveolus walls break down, reducing the surface area for gas exchange. Carcinogens in tar can cause lung cancer.

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