Breathing in human beings


What is breathing?

Breathing is the process of taking air into the body (lungs) and removing air out of the body.

Breathing is also called gaseous exchange. Gases are moved or exchanged between the body and the atmosphere.

How does breathing help us?

  1. We breathe in to get oxygen in order to keep alive. The air we breath in is rich in oxygen. Oxygen breaks down the food inside our body to release energy. The energy  is used for body functions and for doing work. All body functions need energy.  In the absence of oxygen, the human body cells will die. 
  2. We breath out to remove carbon dioxide from the body. When the body cells work, they releases some chemicals that may be harmful to the cells. For example, when the cells breaks down food in the presence of oxygen to give energy, carbon dioxide is released as a waste material.

NB: Breathing is automatic. 

Parts of the breathing system

The breathing system is made up of the following: 

  1. Nose
  2. Trachea
  3. Diaphragm
  4. Bronchus
  5. Lungs  



This is the opening of the breathing system.

The nose has the following functions:

  • It is the inlet and outlet through which the air enters and leaves the body.
  • It contains mucus and hair both of which trap microorganism and dust from the air, therefore cleaning it before it reaches the lungs.
  • It warms the air entering the body.
  • The nose is the sense organ for the sense of smell. 


The trachea  also called the windpipe. The trachea is the pipe that leads air from the nose into the lungs.

The trachea has tiny hairs called cilia  inside it that move about to sweep out dust particles and mucus, which is then coughed out.

The trachea has C-shaped rings around it to ensure that it stays open all the time to avoid suffocation.

At its lowest end, it divides into two tubes ,bronchi (bronchus singular) each of which leads into one of the lungs.

The left bronchus enters the left lung while the right bronchus enters the right lung.


This is a small finger like membrane that prevents food from entering the windpipe during swallowing.

When we swallow, the epiglottis bends and covers the entrance to the windpipe.


These are the spongy and elastic organs located in the chest or rib cage.

Characteristics of lungs:

  • They are elastic that is can expand to take-in air or compress to expel air.
  • They are spongy,because they are made of very many air sacs called alveoli.

The alveoli holds the air. The alveoli are covered by blood vessels to allow for the movement of air into and out of blood. The blood releases its carbon dioxide into the air sacs.

In turn, oxygen enters into the blood from the air sacs. This means that the blood leaving the lungs and going back to the heart has less carbon dioxide but has a lot of oxygen.

It also means that the blood coming to the lungs from the heart has a lot of carbon dioxide and little oxygen.


The diaphragm is a curved (bow-shaped) muscle that separates the area around the lungs.

The diaphragm has the ability to contract and relax. When we breathe out, the diaphragm is at rest and is dome-shaped like a bow.

When we breathe in, the diaphragm contracts, loses its bow shape and becomes flat.


The ribs are the curved bones at the side of the chest.

They form the chest cavity or ribcage. Ribs protect the organs inside the ribcage.

Breathing in Human Beings

Breathing in

When breathing in, the following things happen:

  1. The bow-shaped diaphragm contracts thus becoming flat.
  2. The ribcage is moved upwards by the ribs.

Both these occurrences increase the volume of the lungs. This forces the lungs to suck in air.

See the image below

This process is called inspiration or breathing in or inhalation.

The air sucked in has a:

  • High oxygen concentration
  • Low carbon dioxide concentration

Watch the video below to learn more:

Breathing out

When breathing out the following things happen:

  1. The flat diaphragm relaxes and becomes bow-shaped again.
  2. The rib-cage moves downwards and inwards.

Both occurrences decrease the volume of the lungs and so, air is forced out of the lungs through the nose, a process called expiration or exhalation or breathing out.

See the image below:

The expelled air has a:

  • Low oxygen concentration.
  • High carbon dioxide concentration.

Play the video below to learn more:

Watch this video on breathing system


The table below shows the composition of air entering and leaving the lungs.


Inspired air



air composition

Oxygen 20.96% 16.5%
Carbon dioxide 0.03% 4.5%
Nitrogen 79.0% 79.0%

From the table we can see that oxygen is extracted from air breathed in while carbon dioxide is added to the air breathed out. The amount of nitrogen remains the same without increase or decrease.  


Watch this video again 


  • breathing-system by used under CC_BY-SA
  • breathing-system-2 by & eLimu used under CC_BY-SA
  • Anatomy-of-the-nose by & eLimu used under CC_BY-SA
  • Trachea by & eLimu used under CC_BY-SA
  • Epiglottis by & eLimu used under CC_BY-SA
  • lungs by & eLimu used under CC_BY-SA
  • diaphragm by & eLimu used under CC_BY-SA
  • Rib-cage by & eLimu used under CC_BY-SA
  • Breathing-in-and-out by & eLimu used under CC_BY-SA
  • Breathing_system_1 by unknown used under CC_BY-SA
  • Breathing-in-and-out by used under CC_BY-SA
  • Breathing_system_2 by unknown used under CC_BY-SA
  • Breathing_System-The_Epiglottis by unknown used under CC_BY-SA
  • Lungs by used under CC_BY-SA
  • smoke-effect-on-lungs by used under CC_BY-SA
  • Breathing_System-The_Epiglottis_1 by Unknown used under Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License

  • Creative Commons License
    All work unless implicitly stated is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.