Lesson 1 of 5 / Respiration in humans
Follow air into the lungs
Which structures move air, and where do gases actually cross into blood?
I can identify airway structures, alveoli and associated capillaries and state their functions.
I can identify named airways, alveoli and associated capillaries and their functions.Syllabus
Syllabus K224 / K225, Topic 6(a). Identify named airways, alveoli and associated capillaries and their functions.
About 4 min
Make a guess. You are not marked.
Air reaches the alveoli deep in your lungs. Which tubes does it travel through to get there?
Show the answer
Trachea, bronchi, then bronchioles.
Air stays in airways all the way. Capillaries carry blood beside the alveoli, not air.
The key idea
Airways conduct air to alveoli; the closely associated capillaries carry blood past the exchange surface.
Explanation
Air goes through the larynx (voice box) into the trachea. The trachea splits into two bronchi, one going into each lung. These tubes carry air; gases are not exchanged here.
Each bronchus divides into smaller tubes called bronchioles. The bronchioles spread air through the lungs and end in alveoli. Alveoli are tiny air sacs where oxygen and carbon dioxide are exchanged with the blood.
Capillaries wrap closely around the alveoli. They bring blood that is low in oxygen and take away blood that has picked up oxygen. The air stays inside the alveolus and the blood stays inside the capillary. They are side by side, not joined.
Keep three processes apart. Breathing (ventilation) moves air in and out of the lungs. Gas exchange moves gases by diffusion across the walls of the alveoli and capillaries. Respiration releases energy from glucose inside cells.
Step by step
- 1
Trace the air
Air goes through the larynx, trachea, bronchi, bronchioles and then the alveoli.
- 2
Find the blood
Capillaries next to the alveoli carry blood. They do not carry the air you breathe in.
- 3
Name what crosses
Oxygen and carbon dioxide diffuse between the air in the alveoli and the blood.
Worked example
Two routes meet at an exchange surface
Trace air from the larynx to an alveolus, then explain what the nearby capillary carries.
One way to explain it
Air passes through the larynx, trachea, a bronchus and branching bronchioles to alveoli. The nearby capillary carries blood, which gains oxygen by diffusion from alveolar air and loses carbon dioxide to it.
Why this answer works
- Give the airway order.
- Keep blood separate from air.
- Link the adjacent routes through diffusion, not a shared tube.
Watch out for this
A student says: "Air travels through capillaries to reach the alveoli." What is wrong with this?
Show the answer
Air travels through bronchioles to alveoli. Capillaries carry blood beside the alveoli.
Check your understanding
Which route correctly takes inhaled air towards its main gas-exchange surface?
Show the answer
Larynx -> trachea -> bronchi -> bronchioles -> alveoli
Gas exchange occurs across the thin alveolar and capillary walls at the end of this route.
Quick recall
Which structures move air, and where do gases actually cross into blood?