Gas Exchange & Breathing
Describe the structure of the human gas exchange system (trachea, bronchi, bronchioles, alveoli) and explain how the mechanism of breathing — using pressure changes from rib and diaphragm movement — moves air in and out of the lungs
What a learner can do afterwards
- Labels a diagram of the lungs showing trachea, bronchi, bronchioles, and alveoli
- Explains that breathing in lowers air pressure in the chest and air rushes in
- Describes how the structure of alveoli (large surface area, thin walls, good blood supply) aids gas exchange
The lesson
The air you breathe travels down your throat into the trachea, or windpipe. The trachea splits into two tubes called bronchi, one leading into each lung. Inside the lungs, the bronchi branch again and again into thinner tubes called bronchioles, like the branches of a tree getting smaller and smaller.
At the end of each bronchiole sit tiny air sacs called alveoli. They have very thin walls, a huge surface area, and are wrapped in tiny blood vessels. Just like with diffusion, a short distance and a large surface area make gas exchange fast: oxygen crosses into the blood and carbon dioxide crosses out.
Breathing in works by changing the pressure inside your chest. Your diaphragm, a sheet of muscle under your lungs, flattens and pulls down, and your rib muscles pull your ribcage up and out. This makes your chest bigger, so the pressure inside drops below the pressure outside, and air rushes in to even it out.
Breathing out reverses this. Your diaphragm relaxes and curves back upward, your ribs move down and in, your chest gets smaller, and the pressure inside rises above the pressure outside, pushing air back out.
Air flows through the trachea, bronchi, bronchioles, and alveoli, and breathing works by changing the pressure inside your chest so air rushes in or gets pushed out.
Watch it
Where it sits
Learn first
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.