Lungs
Exchange oxygen and carbon dioxide across roughly 500 million alveoli. Breathing is driven mainly by the diaphragm, and the lungs themselves contain no muscle — they are inflated by the chest cavity expanding around them.
Where it is
Chest cavity either side of the heart.
The numbers
- Alveoli
- about 500 million
- Gas-exchange surface
- 50–75 m²
- Breaths per day
- roughly 20,000
- Tidal volume at rest
- about 500 ml
Worth knowing
The left lung is smaller than the right and has two lobes rather than three, because the heart occupies space on that side — the cardiac notch is a literal indentation. The alveolar surface is roughly the floor area of a squash court, folded into a space the size of two footballs.
A common claim that is wrong
Lungs do not "pull" air in. Air is pushed in by atmospheric pressure once the diaphragm lowers and the chest volume increases — which is why a punctured chest cavity stops the lung inflating even though the lung is undamaged.
Structural reference only — this is not medical advice, and individual variation in every figure here is substantial. Anything concerning your own health belongs with a clinician rather than a reference page.
Common questions
- What does the lungs do?
- Exchange oxygen and carbon dioxide across roughly 500 million alveoli.
- Lungs — key numbers
- Alveoli: about 500 million. Gas-exchange surface: 50–75 m². Breaths per day: roughly 20,000. Tidal volume at rest: about 500 ml.
- Is it true that…
- Lungs do not "pull" air in. Air is pushed in by atmospheric pressure once the diaphragm lowers and the chest volume increases — which is why a punctured chest cavity stops the lung inflating even though the lung is undamaged.
Related pages
- Heart A four-chambered pump, roughly fist-sized, beating about 100,000 times a day.
- Brain About 1.4 kg, using roughly 20% of the body’s energy at 2% of its mass.
- Liver The largest internal organ, around 1.5 kg, and the only one that regenerates.
- Skin The largest organ — about 2 m² and 4 kg in an adult.
- Kidneys Two fist-sized filters processing about 180 litres of blood a day.
- Bones Bones
- Blood types Blood
- Teeth Teeth
- Blood Blood
- The senses Senses
- Taste Senses
Sources
- Typical range compiled from manufacturer specifications — At One Place