TH1.H2.5 Alveoli Walls
Alveolar Walls:
- Alveolar walls are very thin
- The distance between the lumen of the alveolus and the lumen of the capillary, which lies in the alveolar wall, is mostly
- The alveolus is lined by a simple epithelium
- There are two types of epithelial cells which make up the epithelial lining of the alveolus:
- Type I alveolar cells
- These are squamous epithelial cells and form the majority of the cells lining the alveolus
- It is across these cells that gaseous exchange takes place
- Type II alveolar cells (great alveolar cells)
- These are large polygonal cells
- They are responsible for the production and release of a phospholipid lrnown as surfactant
- Surfactant forms a thin layer on the luminal surface of the alveolar cells (and the cells lining the respiratory bronchioles)
- It is a moisturiser of the luminal surface of the epithelium - this helps the passage of gasses - and also reduces the surface tension on the alveolar walls
- The epithelial cells rest on a basement membrane
- Mostly, this is fused with the basement membrane of the endothelial cells of the capillaries which lie in the centre of the alveolar wall
- A small amount of fine connective tissue, including elastic fibres, is found in the alveolar walls
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