The big idea: Emphysema is a lung disease in which the walls between alveoli are destroyed, so gas exchange becomes far less efficient.
Why this matters
- The lungs exchange gases at millions of tiny air sacs called alveoli
- Their thin walls and huge total surface area let oxygen diffuse quickly into the blood
- In emphysema, neighbouring sacs merge into fewer, larger air spaces
- So the lung has a much smaller surface area for gas exchange
A healthy alveolus: a small, thin-walled air sac pressed against a capillary — many of these give a huge surface area for fast gas exchange. Emphysema destroys these walls, so the sacs merge into fewer, larger spaces with far less surface area.
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- Alveolus (plural: alveoli)
- A tiny air sac in the lung where gas exchange happens; its wall is just one cell thick. Millions of alveoli give the lung a very large surface area.
- Surface area for gas exchange
- The total area of alveolar wall across which oxygen and carbon dioxide can diffuse. The larger it is, the faster gases can be exchanged.
- Emphysema
- A lung disease in which the walls between alveoli are broken down, so the sacs merge into fewer, larger spaces with a much smaller surface area for gas exchange.
- Elastic recoil
- The ability of healthy lung tissue to spring back to its smaller shape, helping to push air out when you breathe out. Emphysema destroys this.
Why this matters: Gas exchange depends on a large surface area, a short diffusion distance and a steep concentration gradient.
Emphysema attacks the first two: it shrinks the surface area and damages the thin walls, so oxygen can no longer diffuse into the blood fast enough.
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Emphysema is usually caused by long-term irritation of the lungs, most often from cigarette smoke (and from air pollution).
The damage follows a clear chain: the irritation breaks down alveolar walls, which reduces the surface area, which slows oxygen uptake, which leaves the person breathless.
The cause-and-effect chain
Walls destroyed
The thin walls between neighbouring alveoli break down.
Sacs merge
Many small sacs become fewer, larger air spaces.
Surface area falls
There is far less area for oxygen to diffuse across.
Recoil lost
The lung can no longer spring back, so air is trapped and breathing out is hard.
Result
Oxygen reaches the blood too slowly, so the person is breathless and tires quickly.
| Step in emphysema | What happens | Why it impairs gas exchange |
|---|---|---|
| 1. Trigger | Long-term irritation, most often from cigarette smoke | Causes inflammation that damages the lung tissue |
| 2. Walls destroyed | The thin walls between neighbouring alveoli are broken down | Small sacs merge into fewer, larger air spaces |
| 3. Surface area falls | Total surface area for diffusion is greatly reduced | Less area means less oxygen can diffuse per breath |
| 4. Recoil lost | The lung loses its elastic recoil | Air is trapped; it is harder to push old air out and draw fresh air in |
| 5. Outcome | Oxygen uptake into the blood is too slow | The person becomes breathless and cannot exercise as before |
Two effects, not one: Emphysema hurts gas exchange in two ways at once:
It reduces the surface area (fewer, larger sacs), and it loses the elastic recoil (so stale, low-oxygen air is trapped in the lungs).
Both mean less oxygen enters the blood per breath — a strong answer names both.
Healthy lung
- Many small alveoli → large surface area
- Walls one cell thick → short diffusion distance
- Good elastic recoil → air pushed out easily
- Oxygen uptake keeps up with demand
Lung with emphysema
- Fewer, larger spaces → small surface area
- Walls damaged → longer / poorer diffusion
- Lost elastic recoil → air trapped, hard to exhale
- Oxygen uptake too slow → breathlessness
A memory hook: Think 'fewer, bigger, slower': emphysema makes fewer, bigger air sacs, so gas exchange becomes slower.
Less surface area + trapped air = not enough oxygen.
Risk factors and prevention: The biggest cause of emphysema is smoking; air pollution also contributes.
So the public-health changes most likely to reduce emphysema target these: anti-smoking laws, stop-smoking support, and cutting air pollution.
This 'how to reduce incidence' angle is a favourite quick exam point.
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How this is tested: Emphysema is tested on Papers 1A, 2 and 3. Score by chaining cause to effect.
| Paper | What you are asked | How to score |
|---|---|---|
| Paper 2 4-mark Explain | The changes in lung function seen in emphysema | Chain cause to effect: walls destroyed → fewer, larger sacs → less surface area + lost recoil → slower oxygen uptake → breathlessness |
| Paper 3 2-mark Predict | How emphysema would change a person's response to moderate exercise | They cannot raise oxygen uptake enough, so they become breathless and tire quickly |
| Paper 1A single mark | A micrograph: the direct effect of alveolar destruction; or which national changes would most reduce emphysema | Reduced surface area; reduce smoking / pollution |
IB-style question — explain the changes in lung function
Explain the changes in lung function seen in a person with emphysema. [4]
How to score all four marks
- Start with the damage. The walls between alveoli are broken down, so many small sacs merge into fewer, larger air spaces.
- Link to surface area. This reduces the total surface area available for gas exchange.
- Link to diffusion. With less surface area (and a longer / damaged diffusion path), oxygen diffuses into the blood more slowly, so the blood is less well oxygenated.
- Add the recoil effect. The lung also loses its elastic recoil, so air is trapped and it is harder to exhale — together these make the person breathless and easily tired. (Award 1 mark per distinct point, up to 4.)
Final answer
Alveolar walls are destroyed, so sacs merge into fewer, larger spaces; this reduces the surface area for gas exchange, slowing oxygen uptake into the blood; the lung also loses elastic recoil, trapping air and making exhaling harder — so the person becomes breathless.
Why this scores full marks: Each step is a separate scoring point in a logical chain — damaged walls, less surface area, slower diffusion, lost recoil.
An Explain [4] needs the links between cause and effect, not just 'the lungs are damaged' written four ways.
| Feature | Healthy lung | Lung with emphysema |
|---|---|---|
| Alveoli | Many small, separate air sacs | Walls broken down — sacs merge into fewer, larger spaces |
| Surface area for gas exchange | Very large | Greatly reduced |
| Diffusion distance | Short (walls one cell thick) | Longer / damaged in places |
| Elastic recoil (springs back to push air out) | Good — exhaling is easy | Lost — air is trapped, exhaling is hard |
| Oxygen uptake into the blood | Fast enough to meet demand | Too slow — blood is poorly oxygenated |
| Effect on the person | Normal breathing and exercise | Breathlessness, tires quickly, limited exercise |