The gas exchange system and airways
The gas exchange system
- 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 (windpipe) → into two bronchi (one per lung) → into many bronchioles → into tiny alveoli.
- Each alveolus is wrapped in a network of capillaries, bringing air and blood very close together.
Practice
Put the airways in the order air passes through them.
Air flows: trachea → bronchi → bronchioles → alveoli (where exchange happens).
Airway tissues
| Tissue | Function |
|---|---|
| cartilage | C-shaped rings hold the airway open |
| ciliated epithelium | cilia beat to sweep mucus up to the throat |
| goblet cells | 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 | very thin alveolus lining → short distance to cross |
Practice
The C-shaped rings of cartilage in the trachea and bronchi:
Cartilage supports the airway, keeping it open as air pressure changes during breathing.
Practice
Goblet cells in the airway lining:
Goblet cells secrete mucus to trap inhaled dust and microbes; cilia then sweep it away.
Practice
The squamous epithelium of the alveoli is very thin and flat because this:
A thin, flat lining means a short diffusion distance, so gas exchange is fast.
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.
Practice
How do cilia help keep the lungs clean?
Cilia beat in a wave, moving the dirt-laden mucus up and out of the lungs.
You've got it
Key idea
- 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