Anatomy & Physiology › Section T · The respiratory system › Topic T.3
Gas exchange
Breathing only brings air to the alveoli; the exchange itself is pure diffusion, with no pumps and no energy spent. This topic uses two gas laws to explain why oxygen moves into blood and carbon dioxide moves out, and how the lungs match air flow to blood flow so that little effort is wasted.
In this topic
- Two sites, one mechanism
- Dalton's law and partial pressure
- Worked example: the partial pressures of air
- Henry's law and solubility
- Alveolar air is not fresh air
- Worked example: from inspired air to alveolar oxygen
- Exchange in the lungs and the tissues
- Worked example: why a small CO₂ gradient is enough
- What limits diffusion
- Common mistakes to avoid
- Key takeaways
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