How your lungs work: a quick tour
You take around 20,000 breaths a day without thinking about it. Here's what happens on each one.
The airway
Air enters through your nose or mouth. Your nose is the better route: it warms, humidifies and filters the air, trapping dust and pollen in mucus and tiny hairs.
From there, air passes down your throat, through your voice box (larynx) and into your windpipe (trachea). The trachea splits into two main airways, the bronchi, one for each lung. These branch again and again into smaller tubes called bronchioles, like an upside-down tree.
The air sacs
At the end of the smallest branches are clusters of tiny air sacs called alveoli. You have hundreds of millions of them. Spread flat, their surface would cover roughly the area of a tennis court.
Each alveolus is wrapped in tiny blood vessels (capillaries). The wall between the air and the blood is extremely thin, so:
- Oxygen moves from the air into your blood, where it attaches to hemoglobin in your red blood cells.
- Carbon dioxide, a waste product, moves from your blood into the air, and you breathe it out.
The muscles that do the work
Your lungs don't have muscles of their own. The main breathing muscle is the diaphragm, a dome-shaped sheet under your lungs. When it contracts and flattens, your chest expands and air flows in. When it relaxes, air flows out. Muscles between your ribs help, especially during exercise.
Your lungs' self-cleaning system
The airways are lined with mucus and millions of tiny hair-like structures called cilia. The cilia sweep mucus, along with trapped dust and germs, up toward your throat, where you swallow or cough it out. Smoking damages this system, which is one reason smokers cough more.
What can go wrong
- Airways narrow, as in asthma (Asthma basics)
- Airways and air sacs are damaged, as in COPD (COPD early signs)
- Infection, such as pneumonia
- Breathing is disrupted during sleep, as in sleep apnea
Looking after them
Don't smoke or vape, stay active, keep up with vaccines your doctor recommends, and pay attention to air quality. See Breathing exercises for better lung health.