Читать книгу Understanding Anatomy and Physiology in Nursing - John Knight - Страница 162

The alveoli (alveolus = singular) are thin-walled, sac-like structures composed of two major cell types. Type I cells are thin, flat, squamous epithelial cells which make up around 95 per cent of the alveolar wall. These cells are elastic in nature, allowing each alveolus to inflate (like a balloon) during inspiration. The alveolar wall is incredibly delicate with a width as thin as 0.2 μm, which is roughly the same thickness as the wall of a soap bubble. The remaining 5 per cent of the alveolar wall is made up of type II alveolar cells which secrete a material called pulmonary surfactant, which reduces the surface tension of the alveoli to allow easier inflation. Without this surfactant alveolar wall, lung inflation would be extremely difficult, if not impossible.