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Biology
How do lungs work?
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Explore a breath: breathing muscles change pressure and drive air into and out of the lungs.
Five lung lobes, the bronchial tree, an open anterior rib cage and the diaphragm. Anchored labels show pressure, volume and the cause of airflow.
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Changing a condition restarts the breath for comparison.
Airflow
Run one breath and watch the purple diaphragm. As it contracts, its dome lowers, the chest expands and the lungs follow.
Air remains in the lungs after exhaling. Illustrative model values.
Maximum added air
Try a narrow airway at the same time point. Airflow and inflation change even though muscle effort is unchanged.
Lungs
Both lungs contain small airways and alveoli. They follow chest expansion through pleural coupling and do not contract as muscles.
Anatomy: Z-Anatomy / BodyParts3D · CC BY-SA · CC BY-SA 4.0
Model notes
- A single elastic compartment illustrates spontaneous ventilation. Lungs do not contract as muscles: the diaphragm and intercostal muscles change chest volume, and pleural coupling expands the lungs. Exhalation here is passive.
- Muscle effort, airway width and ease of expansion are relative indices. Compliance represents the whole respiratory system. Resistance proportional to the inverse fourth power of width approximates ideal flow. These values do not assess an individual's health.
- Displayed volume is air added above the resting end-expiratory level. The lungs retain baseline air (2.5 L in this model). Outside air pressure is the zero-Pa reference. The pressure difference determines airflow direction. The pressure bar keeps the same ±250 Pa scale; // marks a value beyond the scale, while the Pa number remains the true value.
- Anatomy is selectively adapted from Z-Anatomy/BodyParts3D; deformation is illustrative, not a detailed model of pleural mechanics. The anterior ribs are partly cut away to reveal the inside. Arrows represent all air, not only oxygen or carbon dioxide. Gas exchange, blood flow and disease are outside this model.
- One breath is slowed for observation: contract, hold contraction, then relax. A narrow airway may retain some added air after 10 seconds. Replay starts from baseline to compare equal starting conditions.