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Why tiny air sacs stay open

Science · The Human Body · ages 20-21

Name ______________________ Date ____________

What does surfactant do?
- Thickens the sac walls
- Lowers the film tension so small sacs stay open
- Stops blood flow
What makes air flow into the lungs?
- Chest expansion dropping pressure below outside air
- Blood pushing air inward
- The nose heating the air
Muscles pay for the in breath while elastic recoil refunds much of the out breath.
Circle one: True False
A loop plot shows a very wide area for each breath. What follows?
- Each breath costs much work
- Breathing is cheap and easy
- Compliance must be high
Two lungs take the same breath, but one needs double the pressure swing. What does that mean?
- It is stretchier
- It has more surfactant
- Stiff, low compliance
A newborn lacks surfactant. Which sacs collapse first?
- The largest sacs
- The smallest sacs
- All sacs equally at once
Raising the pressure swing always fixes low air delivery with no extra cost.
Circle one: True False
Extra push moves barely any extra air in a scarred lung. What is wrong?
- The airways are too wide
- Surfactant is overabundant
- The tissue is stiff, so compliance has fallen

Answer key

For grown-ups. Fold this page away before handing over the rest.

Lowers the film tension so small sacs stay open · The soapy film cuts tension where collapse threatens most.
Chest expansion dropping pressure below outside air · Wider cavity means lower pressure, so outside air flows in.
True · Widening costs effort, and relaxing gives air back.
Each breath costs much work · Loop area is work, so wide means tiring.
Stiff, low compliance · Less stretch per push means a flatter slope and lower compliance.
The smallest sacs · Collapse pressure runs highest in the tiniest bubbles.
False · Bigger swings cost more work each breath and tire muscles.
The tissue is stiff, so compliance has fallen · Flat slope means pushes buy little stretch.