Exhaled air vs inhaled air

• Air which enters the lungs (inhaled air) is different in several regards to air that is passed out (exhaled air)
• Exhaled air contains less oxygen and more carbon dioxide.
• It is also warmer and more moist.

• Nitrogen is not absorbed by plants or animals.
• Inhaled air has more oxygen and less carbon dioxide when compared to exhaled air.

An air sac. Image credit wordpress.com

• The composition of inhaled air changes in the alveoli.
• This is where gas exchange takes place.
• Each alveolus is a microscopic structure with capillaries .
• The air in the alveoli has more oxygen than the blood around them.
• The oxygen diffuses into the blood.
• There is more carbon dioxide in the blood than in the alveoli so it diffuses from the blood into the air sacs.
• This two way diffusion is called gas exchange.
• This happens in millions of air sacs every minute of everyday.
• The breathing process makes sure that there is a higher concentration of oxygen in the air sacs that in the blood.
• This means that oxygen will always diffuse into the blood and carbon dioxide outside the blood.

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