Exchange surfaces - Alveoli in the Lungs

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Exchange Surfaces

Exchange surfaces are made more effective by having;

  • Having a large surface area.
  • Being thin, thereby decreasing the diffusion distance.
  • Having an efficient blood supply.
  • For gas excahnge, animals should also be well ventilated. 
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Alveoli

The Alveoli are small sacs in the lungs. This is where the exchange of Carbon Dioxide and Oxygen takes place. A single Alveolus has a single layer of cells.

As there are thousands of Alveoli in the lungs a large surface area is created making the gas exchange more efficient.

A single alveoli is surrounded by a blood network, a blood capillary with a single celled wall, carrying blood with a very high concentration of Carbon Dioxide and a low concentration of Oxygen. This has been carried from the body tissues via the heart.

The alveoli can be ventilated by the person breathing in and out. The inhaled air has a high concentration of oxygen and a low concentration of carbon dioxide. 

Oxygen can then move by diffusion from the air into the blood and the Carbon Dioxide can move to the air from the blood. 

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Inhaled and Exhaled Air

Inhaled air

  • Nitrogen - 78%
  • Oxygen - 21%
  • Carbon Dioxide - 0.04%

Exhaled air

  • Nitrogen - 79%
  • Oxygen - 16%
  • Carbon Dioxide - 4%
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