Alveolar-capillary barrier

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The alveolar-capillary barrier exists in the gas exchanging region of the lungs. It exists to prevent air bubbles from forming in the blood. and from blood entering the alvioli. It is formed by the type 1 pneumocytes of the alveolar wall, the endothelial cells of the capillaries and the basement membrane between the two cells. The barrier is permeable to molecular oxygen, carbon dioxide, carbon monoxide and many other gasses.

This blood gas barrier is extremely thin (0.2-0.4) nm so as to allow sufficient oxygen perfusion, yet it is extremely strong. This strength comes from the type 4 collegen in between the endo and epitheliam cells. Damage can occur to this barrier at pressures of around 40mmhg. Failure of the barrier is often seen in thoroughbred race horses due to their selective breathing.


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