The gas exchange system and airways
Introduced| English | Meaning |
|---|---|
| trachea/trəˈkɪə/ | The airway connecting the larynx to the bronchi in humans and other vertebrates. |
| bronchi/ˈbrɒŋkaɪ/ | Airways branching from the trachea and dividing within the lungs into smaller passages. |
| bronchiole/ˈbrɒŋkɪəʊl/ | A small branching airway within the lung that leads towards the gas-exchange regions. |
| alveoli/ˈælvɪɒli/ | Tiny air sacs in the lungs where gases are exchanged between air and blood. |
| cartilage/ˈkɑːtɪlɪdʒ/ | The firm flexible tissue in rings that holds the trachea and bronchi open. |
| ciliated epithelium/ˈsɪlɪeɪtɪd ˌepɪˈθiːlɪəm/ | A lining of cells bearing tiny hairs (cilia) that sweep mucus along airways. |
| mucus/ˈmjuːkəs/ | A slippery secretion that protects and lubricates surfaces and can trap particles and pathogens. |
| goblet cell/ˈɡɒblət sel/ | A specialised epithelial cell that produces and releases mucus. |
| squamous epithelium/ˈskwɒməs ˌepɪˈθiːlɪəm/ | A single layer of flat cells forming a thin exchange surface, as in the alveoli. |
Getting oxygen to the blood
- Your body must take in oxygen and get rid of carbon dioxide.
- Air travels down a branching set of airways to tiny sacs deep in the lungs.
- Special tissues keep those airways open and clean.
The path of air
- Air goes: down the trachea 气管 (windpipe) → into two bronchi 支气管 (one per lung) → into many bronchioles 细支气管 → into tiny alveoli 肺泡.
- Each alveolus is wrapped in a network of capillaries, bringing air and blood very close together.
The human lungs, where gas exchange takes place across millions of alveoli.
Explore the airways
Tap each part. Air branches from the trachea down to the tiny alveoli, where gas exchange happens.
Put the airways in the order air passes through them.
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Air flows: trachea → bronchi → bronchioles → alveoli (where exchange happens).
Airway tissues
| Tissue | Function |
|---|---|
| cartilage 软骨 | C-shaped rings hold the airway open |
| ciliated epithelium 纤毛上皮 | cilia beat to sweep mucus 黏液 up to the throat |
| goblet cells 杯状细胞 | make mucus that traps dust and microbes |
| smooth muscle | contracts to narrow the airway |
| elastic fibres | stretch on breathing in, recoil to push air out |
| squamous epithelium 扁平上皮 | very thin alveolus lining → short distance to cross |
A section through an airway wall: cartilage, smooth muscle, and the ciliated epithelium with goblet cells
**Lung tissue under the microscope: a small airway in the centre, ringed by the lacy network of thin-walled alveoli **
The C-shaped rings of cartilage in the trachea and bronchi:
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Cartilage supports the airway, keeping it open as air pressure changes during breathing.
Match each airway feature to its job.
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Cartilage supports, goblet cells trap, cilia sweep, and the thin alveolar lining speeds diffusion.
The squamous epithelium of the alveoli is very thin and flat because this:
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A thin, flat lining means a short diffusion distance, so gas exchange is fast.
Bronchioles have no cartilage; their walls contain smooth muscle instead.
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The smallest airways lose the cartilage and have smooth muscle, which can narrow them.
Keeping the lungs clean
- Goblet cells (and mucous glands) make mucus that traps dust and microbes you breathe in.
- The cilia then sweep that mucus up to the throat, where it is swallowed.
- Together they protect the lungs from dirt and infection.
Ciliated epithelium and goblet cells keep the airways clean
The tiny hair-like structures that beat to sweep mucus up out of the lungs are called ______.
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Cilia beat in a wave, moving the dirt-laden mucus up to the throat to be swallowed.
You've got it
- air path: trachea → bronchi → bronchioles → alveoli (wrapped in capillaries)
- cartilage holds airways open; smooth muscle narrows them; elastic fibres recoil
- goblet cells make mucus (traps dust/microbes); cilia sweep it up to the throat
- squamous epithelium = thin alveolus lining → short diffusion distance