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Human gas exchange systems

The mechanism of breathing

The mechanism of breathing

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Tutor: Priya


The mechanism of breathing

​​In a nutshell

Breathing is important as it enables air to flow into and out of the lungs. The process of breathing involves inhaling and exhaling. The amount of air that can fill the lungs is also known as lung volume. Lung volume can be measured with spirometry.


To inhale is to breathe in and to exhale is to breathe out. 

Science; Human gas exchange systems; KS3 Year 7; The mechanism of breathing
A:The process of inhalingB: the process of exhaling1. Top of the diaphragm,  2. Skeletal muscle of the diaphragm.


When you inhale, the diaphragm moves downwards and the ribcage moves upwardsThis causes the volume of the chest cavity to increase. Increasing the volume of the chest cavity causes the pressure to decrease. This decrease in pressure results in the air rushing in to fill the lungs.


When you exhale, the diaphragm moves upwards and the ribcage moves downwardsThis causes the volume in the chest cavity to decrease. This decrease in volume results in an increase in pressure. As a result, increasing the pressure causes air to rush out of the lungs.

Measuring lung volume


Lung volume is the amount of air that can be inhaled into the lungs in a single breath. 

Lung volume can vary between different people. 


Shorter people tend to have smaller lung volumes than taller people. People with conditions affecting the lungs may also have a reduced lung volume over time.


To measure lung volume, a machine called a spirometer is used. To use a spirometer, a person needs to breathe into a tube attached to a machine for a few minutes. The machine records the volume of air that is breathed in and out over time, and plots the results on a special graph called a spirogram.

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FAQs - Frequently Asked Questions

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