what does the alveoli do

The alveoli are tiny air sacs in the lungs where gas exchange happens: oxygen moves into the blood, and carbon dioxide moves out to be exhaled. They also help keep the lungs open, with surfactant preventing the sacs from collapsing.

In simple terms

• You breathe in air.
• Oxygen reaches the alveoli.
• Oxygen passes into nearby capillaries.
• Carbon dioxide passes from the blood into the alveoli and leaves when you breathe out.

Why they matter

Alveoli give the lungs a huge surface area, which makes breathing efficient. Their very thin walls make it easy for gases to cross quickly.

Extra role

Some alveolar cells help repair damage, and immune cells inside the alveoli help remove dust and germs.

TL;DR: Alveoli are the lungs’ tiny exchange units—they bring oxygen into your blood and remove carbon dioxide.