The lungs are the major organs responsible for getting oxygen into the blood and removing carbon dioxide as a person breathes. Breathing is the movement of gases into and out from the lungs, and is also called ‘ventilation’. Breathing in is called ‘inhaling’, and breathing out is called ‘exhaling’.

When a doctor needs to see something inside of your body, they might use an X-ray exam. An X-ray machine makes X-rays and directs them towards you. The X-rays pass through some parts of the body but are blocked by other parts. Solid objects like your bones will show up white while softer substances like your lung tissue or muscles will look grey. The air in your lungs will look black.

Image Credit: Irena Wojsyk-Banaszak and Anna Bręborowicz, University of Medical Sciences, Poznań, Poland and Katarzyna Jończyk-Potoczna (CC BY 3.0 licence)

Plastic model of the lungsPlastic model of the insides of the lungs
SOMSO® models from Adam,Rouilly

A look inside the lungs

Air is drawn into the body through the mouth and nose, and then travels down the trachea (also called the windpipe) into a bronchus (there are two bronchi, leading into each lung). The bronchus then splits into many narrow bronchioles that finally end in the microscopic air sacs called alveoli. This is where gas exchange takes place, oxygen being absorbed into the blood, carbon dioxide moving in the opposite direction. The air is then breathed out.

Slide the arrows on the image to see inside the lungs model.

Image Credit: SOMSO® model from Adam,Rouilly

The lungs are the only organs that can float on water (can you suggest a reason why?)

Horses only breathe through their noses


Here’s a great video explaining how oxygen and carbon dioxide are transferred in the alveoli, along with experiments you can try at home: The gas exchange system in breathing.

BBC Bitesize videos explain breathing



Watch this BBC Bitesize video, which explains why we need to breathe, how that happens, and how the gases are moved around the body: How do humans breathe?


How is breathing rate affected by exercise?

1) Sit quietly for 5 minutes, breathing normally.
2) Count how many breaths you take in 30 seconds (a breath is counted by breathing in and then breathing out).

3) Multiply this number by 2 to find out how many breaths you take at rest.

4) Repeat this two more times (give yourself a short break between each count) so that you have 3 values.
5) Add your 3 values together and divide by 3 to find out your average breathing rate (breaths per minute).

6) Now carry out 2 minutes of intense exercise (such as running on the spot).
7) Sit down immediately, and count the number of breaths per 30 seconds (and then multiply by 2 to discover the new breathing rate).

How has the rate changed? Can you think of a reason why this might have happened?

You can go to the previous PostcardsFromTheBody secret pages by clicking the places below.

MouthStomachSmall Intestine
Photo of PostcardFromThe Mouth
Large IntestineBloodHeart