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Exchange of gases in the Lungs

 

Breathing is a gas exchange mechanism.  Your Lungs help to do just that!  They contain millions of  tiny air pockets called ALVEOLI (air sacs)  which are adapted to maximise the diffusion of carbon dioxide and oxygen (see diagram below).  Alveoli are good at gas exchange because they have:

 

  • a large surface area.  If all the air sacs were flattened out, they would cover an area of 100m2.
  • moist surface which speed up diffusion.
  • very thin walls (just one cell thick) which speeds up diffusion.
  • lots of blood capillaries to carry the gasses.
  • many blood capillaries which help the diffusion O2 and CO2 as their walls are only one cell thick.

 

 

In the alveolus (single air sac) oxygen passes from a high concentration (loads of oxygen) through the thin wall into the blood capillary where there is a low concentration (very little oxygen) .  This is called diffusion, because oxygen is moving from high concentration to low concentration.  When blood returns to lungs it has high concentration of carbon dioxide, so CO2 diffuses out of the blood into the alveolus.

Lung Alveoli

Alveoli Diagram

Note: Deoxygenated blood appears blue in this diagram for explanation purposes only.

Inhaled & exhaled air

Gas

Atmospheric air

Exhaled air

Change

Oxygen, O2

21%

16%

-5%

Carbon dioxide, CO2

0.04%

4%

+4%

Nitrogen, N2

78%

79%

+1%

Others

1%

1%

0%

 

When compared to atmospheric air, exhaled air contains:

  • More CO2 (Carbon dioxide)
  • Less O2 (Oxygen)
  • Slightly more Nitrogen

 

Tags:Diffusion, Lung diffusion, Exchange of gases, Alveoli, Lung cells

 

 

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