The human body
The lungs and airways
The airways conduct air to the lungs, where oxygen and carbon dioxide move between air and blood. Breathing depends on pressure changes produced by respiratory muscles.
The lungs
Two spongy organs filling most of the chest. In hundreds of millions of tiny air sacs (about 480 million on average), oxygen passes into the blood and carbon dioxide passes out.
- MeasuredAir sacs: about 480 million on average (274–790 million), each about 0.2 mm across
- MeasuredSurface for gas exchange: 143 ± 12 m²
- MeasuredTotal lung capacity: 7.0 L in men, 5.0 L in women
The trachea
The main airway connecting the larynx to the bronchi. Its cartilage supports keep the airway open during breathing.
- MeasuredLength: about 12 cm (about 4 cm in newborns)
- MeasuredInside width: 17 mm front to back, 15 mm side to side
- MeasuredNormal side-to-side width at ages 20–79: 13–25 mm in men, 10–21 mm in women
The larynx
The voice box, at the top of the windpipe. Air passing over its vocal folds makes them vibrate, which makes your voice, and it closes during swallowing to keep food out of the airway.
- MeasuredMass: 28 g in men, 19 g in women
The diaphragm
A dome-shaped muscle under the lungs that separates the chest from the belly. When it tightens it flattens and moves down, making room for air to rush into the lungs; it is the main muscle you breathe with.
- MeasuredContracts about 12 times a minute at rest
In Endo-View
In the human atlas you can peel the body layer by layer down to these organs, turn it, take it apart and click any part for its card.
Every number is labelled measured, an estimate or drawn: how we know.
More of the body
The heart and blood vessels The digestive system The kidneys and the urinary system The brain and the nervous system
The journey to life
What Happens to Sperm After Ejaculation How Sperm Get Through the Cervix: Cervical Mucus Sperm in the Uterus: The Race and the White Blood Cells Sperm in the Fallopian Tube: Waiting for the Egg The Human Egg Cell: Its Size and Its Layers How Fertilisation Works: Sperm Meets Egg The Zygote and the First Cell Divisions What Is a Blastocyst? Days 3 to 6 How Implantation Works: Days 6 to 12 The Fetus from Week 10 to Week 20 Pregnancy Week by Week: The Fetus to Week 40 How Birth Works: Labour and the First Breath The Embryo Week by Week: Weeks 4 to 10