Effects of Smoking: Looking After Your Amazing Lungs
Hello, young scientists! Right now you are breathing about 12 to 20 times a minute without even thinking about it. Every breath brings in the oxygen your cells need to release energy from food.
In this chapter you will learn: (1) the main parts of the breathing system, (2) how gases are swapped in tiny air sacs, (3) the harmful substances in cigarette smoke, (4) how smoking damages gas exchange, and (5) the health risks of smoking. This science will help you make smart, informed choices.
1. Your Breathing System: A Quick Tour
Your breathing system brings air into your body and takes waste gas out. (See the chapter "Gas exchange in plants and animals" for more detail.)
The air's journey
1. Nose (nasal cavity) – Hairs and sticky mucus trap dust and germs. The air is warmed and moistened.
2. Trachea (windpipe) – A tube in the neck. Rings of cartilage keep it open, like the rings of a vacuum cleaner hose.
3. Bronchi (one is a bronchus) – The trachea splits into two bronchi, one into each lung.
4. Bronchioles – The bronchi branch again and again into tiny tubes, like the branches of a tree.
5. Air sacs (alveoli) – Each bronchiole ends in a bunch of tiny, balloon-like air sacs. This is where gas exchange happens.
Memory aid: "Nice Trains Bring Better Air" = Nose, Trachea, Bronchi, Bronchioles, Air sacs.
The lungs and the parts that move them
Lungs – Two soft, spongy organs in the chest, full of air passages and air sacs.
Rib cage – The ribs and the muscles between them. It protects the lungs and heart, and moves up and out when you breathe in.
Diaphragm – A dome-shaped sheet of muscle under the lungs. It flattens when you breathe in, making more space in the chest.
The cleaning crew: mucus and cilia
The trachea and bronchi are lined with cells that make mucus and cells with tiny hairs called cilia. Mucus traps dust and germs. The cilia beat like a Mexican wave in a stadium, sweeping the dirty mucus up to the throat to be swallowed or coughed out.
Key takeaway: Air travels from the nose to the trachea, bronchi, bronchioles and finally the air sacs. Mucus and cilia keep the airways clean.
2. Gas Exchange in the Air Sacs
What happens in an air sac?
Each air sac is wrapped in a net of tiny blood vessels called blood capillaries. Gases move by diffusion: particles spread from where they are more concentrated to where they are less concentrated.
Oxygen – Air in the air sac has more oxygen than the blood arriving at the lungs. Oxygen diffuses into the blood, and red blood cells carry it to all body cells.
Carbon dioxide – Blood arriving at the lungs carries carbon dioxide made by body cells. It diffuses from the blood into the air sac and is breathed out.
Why are air sacs so good at gas exchange?
1. Thin walls – The air sac wall and the capillary wall are each only one cell thick, so gases travel a very short distance.
2. Large surface area – There are hundreds of millions of air sacs. Together their surface is dozens of times larger than your skin. Like an MTR station with many ticket gates, more surface lets more gas through at once.
3. Rich blood supply – A dense network of capillaries surrounds every air sac. Flowing blood keeps carrying oxygen away and bringing carbon dioxide in.
4. Moist lining – A thin layer of moisture lets oxygen dissolve before it diffuses into the blood.
Did you know? Your right lung has three sections (lobes) but your left lung has only two. The left lung is smaller to leave room for your heart!
Key takeaway: Oxygen diffuses from the air sacs into the blood; carbon dioxide diffuses the other way. Thin walls, a large surface area, a rich blood supply and a moist lining make this fast.
3. What Is in Cigarette Smoke?
Cigarette smoke contains thousands of chemicals. Many are poisonous and dozens are known to cause cancer.
Nicotine – the addictive drug
Nicotine reaches the brain within seconds. It is addictive: the body comes to depend on it, so smokers get strong cravings and find it hard to stop. It also speeds up the heart and raises blood pressure.
Tar – the sticky cancer-causer
Tar is a sticky, brown substance containing many carcinogens (cancer-causing chemicals). It settles on the airways and air sacs, clogging them, and stains teeth and fingers yellow-brown.
Carbon monoxide – the oxygen thief
Carbon monoxide is a poisonous gas with no colour or smell (it is also in car exhaust). It combines with red blood cells much more easily than oxygen does, so the blood carries less oxygen and the heart must work harder.
Irritants – the troublemakers
Irritants irritate the lining of the airways. They cause extra mucus, damage the cilia and trigger coughing.
Try it: the smoking machine
Your teacher may show a "smoking machine" in a fume cupboard. A pump draws smoke through cotton wool and then universal indicator. The cotton wool turns yellow-brown (tar), and the indicator turns from green to yellow or orange because the smoke is acidic.
Key takeaway: Nicotine is addictive, tar causes cancer and clogs air sacs, carbon monoxide reduces the oxygen carried by the blood, and irritants cause mucus and coughing.
4. How Smoking Affects Gas Exchange
Damage to the cleaning crew
Smoke damages the cilia and makes the airways produce more mucus. The dirty mucus builds up and narrows the airways, so smokers cough to clear it ("smoker's cough"). Trapped germs make chest infections more likely.
Damage to the air sacs
Tar coats the air sacs. Over time, the thin walls between air sacs break down, and many small air sacs join into fewer, larger spaces. This reduces the surface area, so less oxygen enters the blood. Think of many small balloons merging into a few big bags: there is less "skin" in total.
Less oxygen carried by the blood
Carbon monoxide takes over part of the red blood cells, so even the oxygen that gets in has fewer places to go. As a result, smokers often get out of breath on stairs or in sports.
Key takeaway: Smoking reduces gas exchange: damaged air sacs (less surface area), damaged cilia with mucus blocking the airways, and carbon monoxide in the blood.
5. Health Risks of Smoking
Lung cancer
Carcinogens in tar can make lung cells divide out of control, forming a lump called a tumour that may spread. Smoking is the main cause of lung cancer, and lung cancer causes more cancer deaths in Hong Kong than any other cancer. Smoking also raises the risk of mouth and throat cancers.
Heart disease and stroke
Nicotine raises heart rate and blood pressure. Chemicals in smoke damage blood vessel linings, so fatty substances build up and narrow the arteries, and clots form more easily. Narrowed arteries to the heart muscle cause coronary heart disease; if one becomes blocked, it causes a heart attack. A blocked or burst blood vessel in the brain causes a stroke.
Emphysema and chronic bronchitis
Emphysema – Air sac walls break down, leaving much less surface area. Patients are breathless even at rest.
Chronic bronchitis – The bronchi stay inflamed and full of mucus, causing a long-lasting cough.
Together these are called chronic obstructive pulmonary disease (COPD). The damage cannot be fully reversed.
Other harmful effects
Smoking also causes yellow teeth, bad breath and gum disease. Smoking in pregnancy can harm the baby, e.g. a low birth weight.
What does "risk" mean?
A risk is the chance (probability) that something harmful happens. Not every smoker gets lung cancer, but smokers are many times more likely to than non-smokers, and the risk grows with more cigarettes and more years of smoking.
Key takeaway: Smoking greatly raises the risk of lung cancer, heart disease, stroke, emphysema and chronic bronchitis.
6. Second-hand Smoke and Newer Tobacco Products
Second-hand smoke
Second-hand smoke is smoke breathed in by non-smokers. It includes side-stream smoke from the burning tip (unfiltered) and mainstream smoke breathed out by the smoker. It raises non-smokers' risk of lung cancer and heart disease, and children get more chest infections and asthma attacks. There is no safe level, so Hong Kong law bans smoking in many places, such as restaurants, indoor workplaces and schools.
E-cigarettes and heated tobacco products
E-cigarettes heat a liquid, usually with nicotine and flavourings, into a mist. Heated tobacco products heat tobacco instead of burning it. Both still deliver addictive nicotine and harmful chemicals. Since 2022, Hong Kong has banned the import, manufacture, sale and promotion of these alternative smoking products.
Key takeaway: Smoking harms people nearby too, and e-cigarettes and heated tobacco are not safe.
7. Saying No and Quitting
Why it is hard to stop
Smokers who stop may feel cravings, bad moods and poor concentration for a while. These are withdrawal symptoms caused by nicotine addiction. The best choice is never to start.
The body starts to heal
It is never too late to quit! Within about a day, the carbon monoxide level in the blood falls back to normal. Over weeks and months, breathing gets easier and coughing reduces. Over the years, the risks of heart disease and lung cancer keep falling. Doctors, nicotine patches or gum, and the Department of Health's quit-smoking services can help.
How to say no
If offered a cigarette or e-cigarette, say "No, thanks" firmly, give a reason ("I want to stay fit for basketball"), or walk away.
Key takeaway: Quitting is hard but the body starts to recover soon after. Saying no from the start is easiest.
Common Mistakes
Mistake 1: "Tar makes smoking addictive." – No! Nicotine is addictive. Tar causes cancer and clogs the air sacs.
Mistake 2: "Carbon monoxide blocks the airways." – No! It works in the blood, reducing the oxygen red blood cells carry.
Mistake 3: "In emphysema the air sacs get bigger, so gas exchange increases." – No! Fewer, larger spaces mean a smaller total surface area.
Mistake 4: "E-cigarettes give out only harmless water vapour." – No! They contain nicotine and other harmful chemicals.
Quick Review
1. Breathing system: nose, trachea, bronchi, bronchioles, air sacs, lungs, rib cage, diaphragm.
2. Oxygen diffuses from air sacs into capillaries; carbon dioxide diffuses the other way.
3. Air sacs: thin walls, large surface area, rich blood supply, moist lining.
4. Nicotine is addictive; tar causes cancer; carbon monoxide cuts oxygen transport; irritants cause mucus and coughing.
5. Health risks: lung cancer, heart disease, stroke, emphysema, chronic bronchitis.
6. Second-hand smoke is harmful; Hong Kong bans the sale of e-cigarettes and heated tobacco.
Great work! Your lungs work hard for you every second, so choose a smoke-free life.