Lungenblaeschen

The air sacs are covered by an etch of very fine blood vessels, known as the capillaries [capillaries: approx. 1000 blood vessels = 1 capillary network per air sac]. This is where the gas exchange takes place: exchange of oxygen [O2] from the air sacs and carbon dioxide [CO2] from the blood vessels.

In this process O2 streams [diffusion] from the inhaled air, passes through the wall of the air sacs and through those of the finest blood vessels. In medicine, those layers are grouped as the alveolo capillary membrane.

In the blood the O2 attaches to red blood cells [erythrocytes]. The latter "drives" the O2 through the blood circulation like a cab to every possible destination. To muscles or other organs (heart, brain etc.) the blood delivers O2, nutrients and other important substances and takes away the waste products. The most important waste product is CO2. It is produced in the cells (e.g. muscle cells) whenever the body performs work and also during the organs' usual business. In exchange for oxygen CO2 is attached to the red blood cells and pumped back the same way it came. Having arrived in the capillaries, at the air sacs, it streams through the walls of the blood vessels (creating room for new O2) as well as through the walls of the air sacs and can then be breathed off from there.

Supplementary information

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    Blood Gas Analysis (BGA)

    Read this file if you want to learn more about what the terms "hypercapnia" or "respiratory partial insufficiency" and "hypoxemia" mean.


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    Pulse Oximeter

    Read this file if you want to learn more about how to measure oxygen saturation and what you should consider when using a pulse oximeter.

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