Gas Exchange (Core)
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Gas Exchange (Core). Modified from: Stephen Taylor Why do we need a ventilation system? . We are large organisms . Oxygen cannot diffuse into all our cells directly from the air, nor can waste products be directly

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Gas Exchange (Core)

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Gas exchange core

Gas Exchange (Core)

Modified from: Stephen Taylor

Gas exchange core

Why do we need a ventilation system?

We are large organisms. Oxygen cannot diffuse into all our

cells directly from the air, nor can waste products be directly

ejected from the body. We have specialised organ systems,

which are efficient, but need delivery of nutrients and

removal of waste. The ventilation system ensures the blood

can be the medium for this.

We are land-borne. Gases need moist surfaces (membranes) in

order to diffuse. Our lungs are moist membranes, allowing

oxygen to diffuse into the blood and carbon dioxide

to diffuse out.

The ventilation system maintains a large

concentration gradient between the alveoli and

the blood. The constant flow of past the alveoli brings

blood with a high CO2 concentration and low O2

concentration. Breathing out keeps the CO2 concentration

in the alveoli low, so it diffuses out of the blood.

Breathing in keeps O2 concentration in the alveoli high,

so it diffuses into the blood.

Diagram from:

Gas exchange core

Gas exchange core

Which process(es) of membrane transport are being used in gas exchange at the membranes of the alveoli?

Gas exchange core

Characteristics of the alveoli walls

Characteristics of the alveoli walls

  • The walls of the alveoli consist of a single layer of cells, called epithelium. There are two types of cells in the epithelium:

    • Type I cells are very flattened, about 0,15 µm thick.

    • Type II cells are rounded and secrete surfactant, which coats the inner surface of the alveoli with a film of moisture, preventing collapse of alveoli during expiration and help oxygen to dissolve.

Gas exchange core

  • There is a dense network of blood capillaries between adjacent alveoli. The walls of these capillaries is also composed of flattened cells, about 0,15 µm thick, and it is called endothelium.

  • An extracellular layer of protein gel, called basement membrane, lies between the epithelium of the alveolus and the endothelium of blood capillaries. It is about 0,1µm thick. This is the gas exchange surface.

  • About 0,4 µm in all

Gas exchange core

Modified from:


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