The Respiratory System
Learning Objectives
Students will be able to:
- Identify the major structures of the respiratory system
- Describe the path air takes from nose to alveoli
- Explain how the respiratory system's structure relates to its function
- Compare the branching pattern of airways to other systems
Engage: Breathing By the Numbers
Right now, without thinking about it:
- You're breathing about 12-20 times per minute
- Each breath moves about 500 mL of air
- That's 7-8 liters per minute
- Over 10,000 liters per day
- And about 4 million liters per year!
The Journey of Air
When you breathe in, air travels through a series of increasingly smaller tubes:
| Structure | Diameter | Function |
|---|---|---|
| Nose/Mouth | 2+ cm | Air entry, warming, initial filtering |
| Pharynx | ~2.5 cm | Shared pathway with food |
| Larynx | ~2 cm | Voice box, prevents food entry |
| Trachea | ~2 cm | Main airway to lungs |
| Bronchi | 1-1.5 cm | Branch to each lung |
| Bronchioles | 0.5-1 mm | Smaller branches |
| Alveoli | ~0.2 mm | Gas exchange (the destination!) |
The Branching Pattern
Like an Upside-Down Tree
The respiratory system branches about 23 times from trachea to alveoli. Each branching doubles the number of tubes. That's 223 = over 8 million tiny airways!
Why Branch?
- Increases total surface area
- Slows down air flow
- Allows more time for gas exchange
- Distributes air to all parts of lungs
The Amazing Alveoli
Alveoli = Tiny air sacs where gas exchange happens
alveoli per person
total surface area
wall thickness
Comparison: 70 m² is about the size of a tennis court, but packed into your chest!
Structure Meets Function
| Design Feature | Why It Matters |
|---|---|
| Huge surface area (70 m²) | More area = more gas exchange possible |
| Very thin walls (0.5 μm) | Gases can diffuse quickly |
| Rich blood supply | Blood constantly available to pick up O2 |
| Moist surface | Gases dissolve and move more easily |
| Branching structure | Reaches every part of both lungs |
Activity: Build an Airway Model
Materials:
- Paper or cardboard tubes (paper towel roll = trachea)
- Straws (bronchioles)
- Small balloons or grape-sized balls (alveoli)
- Tape
Instructions:
- Start with the largest tube (trachea)
- Branch into two medium tubes (bronchi)
- Attach straws as bronchioles
- Attach small balloons at the end as alveoli
Discuss:
- Why does each level get smaller?
- What happens to the total number of tubes at each level?
- Where would particles of different sizes get stuck?
Connection to Air Quality
Everything in the air you breathe goes through this system!
- Large particles (PM10) get trapped in upper airways
- Smaller particles (PM2.5) reach deep into bronchioles
- Ultrafine particles can reach alveoli and even enter blood
- The same huge surface area that helps gas exchange also means huge exposure to pollutants
Key Takeaway
The respiratory system is designed to move air efficiently from the outside world to a huge surface area inside your lungs. Air travels through increasingly smaller tubes until it reaches 300 million tiny alveoli where gas exchange occurs. This same efficient design that delivers oxygen also means any particles in the air have a chance to reach deep into your lungs.