Gas exchange

When you breathe in, you take in oxygen and breathe out carbon dioxide. This process is called gas exchange, which happens in your lungs.
Your lungs contain millions of tiny air sacs called alveoli that expand when you breathe in, allowing you to take in a large amount of oxygen.
The oxygen from the air diffuses into your blood and is carried to all the cells in your body.
Your lungs are soft and delicate, so they are protected by the ribcage, which is made up of strong bones.
Key Components of the Respiratory System:

Trachea (windpipe): Air enters your body through your nose or mouth and passes down the trachea.
Bronchi: The trachea splits into two bronchi (one for each lung).
Bronchioles: The bronchi divide into smaller tubes called bronchioles.
Alveoli: Tiny air sacs at the ends of the bronchioles where gas exchange takes place.

The human respiratory system

We breathe in to take in oxygen for respiration, the process that transfers energy to cells.
Respiration also produces carbon dioxide, which needs to be removed from the body. When we breathe out, we exhale carbon dioxide.
The air we breathe in and out contains different amounts of gases. The composition of the air changes as follows:
- Inhaled air: Oxygen 20.96%, Carbon Dioxide 0.04%, Nitrogen 78%, Other gases 1%.
- Exhaled air: Oxygen 16%, Carbon Dioxide 4%, Nitrogen 78%, Other gases 2%.
When you breathe out on a cold surface, like a mirror, you may notice it steams up. This is because the air you exhale contains water vapour.
As the warm water vapour comes into contact with the cold surface, it condenses, turning into tiny droplets that form a mist on the surface.
This happens because water vapour is a waste product of respiration, just like carbon dioxide.

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