Have you ever noticed what encourages the air to move in and out of our lungs? In the previous lesson, we discussed the process of gas exchange in human respiratory system (click here to visit the previous lesson). In this lesson, we will learn about the factors which cause the movement of air.
Breathing Mechanism in Humans:
What is thoracic cavity?
Thoracic cavity is the space between our lungs and the ribs. The change in its volume encourages breathing. Breathing is made up of inspiration (inhale) and expiration (exhale).
Inspiration:
When we breathe in, our diaphragm muscles contract and it flattens (moves down). External intercostal muscles contract and the internal relax, they both are a pair of antagonistic muscles. Sternum (chest bone), also moves up and outwards. This increases the volume of the thoracic cavity, decreasing the pressure inside lungs. Lungs then attract the atmospheric air which moves from high pressure area to low pressure area. And in this way, lungs receive oxygen.
Expiration:
When we breathe out, our diaphragm muscles relax and move upwards. This causes the external muscles to relax and internal to contract causing the sternum to move inwards and downwards so the area of thoracic cavity decreases and the pressure increases. Lungs are compressed so the atmospheric pressure increases. This forces the air inside the lungs to move out to the environment.
Difference between expired and inspired air
These are a few differences between inspired and expired air.
Component | Inspired air | Expired air |
Carbon dioxide | 0.04% | 4% |
Oxygen | 21% | 16.4% |
Nitrogen | 78% | 78% |
Water vapors | Less | More |
Temperature | Variable | Body Temperature 37 C |
Dust | Variable but usually more | Little |
All pictures are taken from google
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