Lesson 4 ·Class 9 · The Respiratory System · Flow Lab
Mechanics of Breathing
Air does not get sucked in — pressure pushes it.
You have no muscles in your lungs. So how does air get in?
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💪 Step 1 of 6 · Muscles contract
For inspiration the diaphragm flattens downward and the external intercostals pull the ribs up and out.
Free play — step through the process at your own pace, and move the slider to see what changes. Switch to when you're ready to test yourself.
Volume up → pressure down → air in. Expiration is the same chain in reverse, and it needs no effort.
What this lesson covers
Challenges to clear
- Advance to the step that actually makes air move.
- Step through one full breath.
The task
You have no muscles in your lungs. So how does air get in?
What this lesson covers
- Muscles contract — For inspiration the diaphragm flattens downward and the external intercostals pull the ribs up and out.
- Chest volume increases — The thoracic cavity gets bigger in every direction.
- Pressure falls — A bigger space for the same air means lower pressure inside the lungs than outside.
- Air flows in — Air moves from the higher pressure outside to the lower pressure inside. It is pushed in, not sucked.
- Muscles relax — For expiration the diaphragm domes up and the ribs drop. The elastic lungs recoil.
- Air flows out — Chest volume falls, pressure inside rises above atmospheric, and air flows out. Quiet expiration is passive.
Hint
Volume up → pressure down → air in. Expiration is the same chain in reverse, and it needs no effort.