Download The way your lungs work

The way your lungs work
You have two lungs, one on either side of your heart. They fill the inside of your chest. In an
adult, each lung weighs about 1lb (0.45kg). However, the right lung is a little larger than the
left because there is more room for it. Your left lung has to share space with your heart.
Two thin layers of tissue, called the pleura, cover each lung. These layers - or membranes slide over each other as you breathe so your lungs can expand and contract. The inside of
your lungs look like a giant sponge. It is a mass of fine tubes, the smallest of which end in tiny
air sacs called the alveoli. There are around 300 million alveoli and if they were spread out
they would cover an area roughly the size of a tennis court.
Alveoli have very thin walls. They are criss-crossed with the finest of blood vessels called
capillaries.
Your lungs are protected by your rib cage. Between your ribs are muscles that are essential for
breathing. Below your lungs is a dome-shaped muscle called the diaphragm. The diaphragm
is an important muscle for breathing.
Why do you breathe?
Every part of your body needs oxygen to survive. It is carried around the body by red
blood cells in your bloodstream. Oxygen cannot get into your blood directly through the
skin, so a complicated system in your lungs absorbs it from the air and transfers it into your
bloodstream.
The way your lungs work
© British Lung Foundation 2015
1
What makes you breathe?
Before birth a baby relies on its mother’s blood for oxygen and its lungs are filled with fluid. From
the moment of birth, a child must draw air into its lungs and get its own oxygen.
Your brain is constantly receiving signals from your body about the amount of oxygen needed.
This depends on how active you are. For example, when you are asleep you need far less oxygen
than if you are running to catch a bus. So you will breathe more slowly.
Once your brain knows how much oxygen is needed, it sends messages along nerves to your
breathing muscles, so that the right amount of air is breathed into your lungs.
When the nerves to your breathing muscles tell you to breathe in, your diaphragm is pulled flat.
At the same time, the muscles between your ribs pull your rib cage upwards and outwards. This
means your lungs have the largest possible space to expand and pull in air.
How do you breathe?
Each time you breathe, air is drawn into your nose or mouth, down through your throat and into
your windpipe, also called your trachea. This windpipe is a tube about four or five inches long in
adults and splits into two smaller air tubes called the bronchi, one of which goes to the left lung
and the other to the right lung.
The air passes down the bronchi which divide another 15 to 25 times into thousands of smaller
airways, called bronchioles, until the air reaches the alveoli (diagram below).
Breathing out is usually just a matter of relaxing your diaphragm and the muscles between the
ribs. This pushes the air out and your lungs return to their resting size.
How does oxygen get into the bloodstream?
Inside the alveoli, oxygen moves across paper-thin
walls to tiny blood cells called capillaries and into
your blood. It is then picked up by a chemical called
haemoglobin in the red blood cells that carry it
round your body. At the same time, waste products
from your body, in the form of carbon dioxide,
come out of the capillaries back into the alveoli,
ready to be breathed out.
Blood with fresh oxygen is carried from your lungs
to the left side of your heart, which pumps blood
around your body through the arteries. Once
the oxygen has been used up, the blood returns
through the veins, to the right side of your heart.
From there it is pumped to your lungs to remove
carbon dioxide and breathe in more oxygen.
The way your lungs work
© British Lung Foundation 2015
Bronchiole
CO2
O2
Blood
vessel
Air sac
Red blood cells
2
What else do the lungs do?
10,000 litres of air move in and out of your lungs every day. Each breath of air carries germs and
other foreign bodies such as pollutants as well as oxygen. As a result the lungs provide a complex
defence system that prevents unwanted materials getting into the body.
Tiny hairs called cilia line the bronchi and help waft unwanted materials up to the mouth. Mucus
produced in the walls of the airways helps to keep them clean and well lubricated. Cells in the
lungs contain enzymes that produce chemical changes in the blood.
The delicate structure of the lungs is beautifully adapted to carry out the complex business of
breathing and, at the same time, helps protect the body from outside attack.
However, the lungs can be damaged by cigarette smoke, air pollution (for example from vehicles)
and occupational dusts and fumes. If the lungs are damaged, it can lead to breathlessness.
Your lungs are very delicate. Remember to take good care of them.
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British Lung Foundation
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Registered charity in England and Wales (326730) and in Scotland (SC038415)
Code: FL27
Version: 2
Last reviewed: February 2015
Due for review: February 2018
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most up to date version of this information and references, call the helpline or
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The way your lungs work
© British Lung Foundation 2015
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