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 100m^2.
• 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.

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

 

 

🫁 Knowledge Check: Lung Diffusion

How well do you know the mechanics of gas exchange? Test yourself below!

1. Diffusion is the movement of particles from...

• Low concentration to high concentration
• High concentration to low concentration
• Inside the cell to outside only

2. Which gas diffuses FROM the blood INTO the alveoli to be breathed out?

• Oxygen
• Nitrogen
• Carbon Dioxide

3. How thick are the walls of the alveoli and the capillaries?

• One cell thick
• Ten cells thick
• They don't have walls

4. What does a "Steep Concentration Gradient" mean in the lungs?

• The lungs are tilted at an angle.
• There is a large difference in gas levels between the air and the blood.
• The blood is moving very slowly.

5. Which adaptation increases the amount of gas that can diffuse at once?

• Thick mucus lining
• A large total surface area
• Smaller lungs

Check Your Answers

1. High to low concentration (It is a passive process).
2. Carbon Dioxide (Waste product of respiration).
3. One cell thick (This provides a very short diffusion distance).
4. A large difference in gas levels (Maintained by breathing and blood flow).
5. A large total surface area (More space for molecules to pass through).

 

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