Lungs (unlabeled) — free printable diagram

What to label on a respiratory system diagram

A blank respiratory system diagram is normally used as a labelling exercise. The parts below trace the path air actually takes on the way in — nose and mouth, down the trachea, into the bronchi, along the bronchioles and finally to the alveoli, where gases are exchanged with the blood. Labelling them in that order is usually easier than labelling them by position on the page.

Nasal cavity

Warms, moistens and filters incoming air

Trachea

The windpipe — held open by rings of cartilage

Bronchi

The two large tubes branching into the left and right lung

Bronchioles

Progressively smaller tubes inside each lung

Alveoli

Tiny air sacs where gas exchange happens

Lungs

The pair of organs housing the airways and alveoli

Diaphragm

Sheet of muscle below the lungs that drives breathing

Ribs

Protect the lungs and move to change chest volume

• Gas exchange happens only in the alveoli. Everything above them — trachea, bronchi, bronchioles — is plumbing that carries air to and from those sacs, which is a distinction students often miss.
• Oxygen passes from the air in the alveoli into the blood, and carbon dioxide passes the other way. Both move by diffusion, from where they are more concentrated to where they are less.
• The alveoli are numerous, thin-walled and richly supplied with blood vessels. Together those three features give a very large surface area and a very short distance to cross, which is what makes the exchange efficient.
• Breathing in is an active movement: the diaphragm contracts and flattens, the ribs move up and out, the chest volume increases and air is drawn in. Breathing out is largely the reverse and is mostly passive at rest.
• The left lung is drawn slightly smaller than the right because the heart occupies space on the left. Students labelling from a diagram often assume the two are identical.
• Breathing and respiration are not the same thing, and the diagram is a good place to make the point: breathing moves air, while respiration is the chemical reaction releasing energy inside cells.