# The Respiratory System
The respiratory system is responsible for gas exchange: getting oxygen into the blood and removing carbon dioxide. The lungs are specially adapted for efficient gas exchange.
1. Structure of the Respiratory System
Pathway of air: nose/mouth → trachea → bronchi → bronchioles → alveoli
| Structure | Feature |
|---|---|
| Trachea | C-shaped cartilage rings (keeps it open) |
| Bronchi | Branch into each lung |
| Bronchioles | Smaller tubes; smooth muscle controls diameter |
| Alveoli | Tiny air sacs; site of gas exchange |
2. Gas Exchange at the Alveoli
Oxygen diffuses from alveoli into blood; CO₂ diffuses from blood into alveoli.
Adaptations for Efficient Gas Exchange
- Large surface area: millions of alveoli
- Thin walls: one cell thick (short diffusion distance)
- Good blood supply: dense capillary network maintains concentration gradient
- Moist lining: gases dissolve before diffusing
- Ventilation: breathing maintains concentration gradient
3. Ventilation (Breathing)
Inhalation
- Intercostal muscles contract → ribs move up and out
- Diaphragm contracts → flattens
- Volume increases → pressure decreases → air rushes in
Exhalation
- Intercostal muscles relax → ribs move down and in
- Diaphragm relaxes → domes up
- Volume decreases → pressure increases → air pushed out
4. Lung Disease
| Disease | Cause | Effect |
|---|---|---|
| Asthma | Allergens trigger inflammation | Bronchioles narrow; difficulty breathing |
| Lung cancer | Smoking (carcinogens) | Uncontrolled cell growth in lungs |
| COPD | Smoking | Alveoli damaged; reduced surface area |
5. Practice Questions
- Describe the pathway of air from the mouth to the alveoli.
- Explain three adaptations of the alveoli for gas exchange.
- Describe the role of the diaphragm during inhalation.
- How does smoking damage the respiratory system?
- Why is ventilation important for maintaining gas exchange?
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Summary
- Gas exchange occurs at alveoli by diffusion
- Alveoli: large surface area, thin walls, good blood supply, moist
- Breathing: diaphragm and intercostal muscles change volume/pressure
- Smoking causes lung cancer, COPD, and other diseases