Alveolar type 1 cell, plasma membrane

In the lung, the alveolar type I cell is directly exposed to these oxidants in the atmosphere and in tobacco smoke. It is also exposed to oxidants in the blood that diffuse through the blood-air barrier. While the resistance of this cell against oxidants is very low, it also constitutes 95% of the alveolar surface area exposed to the inhaled air (Naimark, 1977). The cell membrane of the type I cell is therefore a relatively large target for free radicals in the inhaled air and is very susceptible to peroxidation of the lipids in its membranes. The cell plasma membrane is a critical site of free radical reactions for several reasons. Extracellularly generated free radicals must cross the... 

Figure 11.1 Ultrastructure of the human lung alveolar barrier. The tissue specimen is obtained via lung resection surgery. (A) Section through a septal wall of an alveolus. The wall is lined by a thin cellular layer formed by alveolar epithelial type I cells (ATI). Connective tissues (ct) separate ATI cells from the capillary endothelium (en) within which an erythrocyte (er) and granulocyte (gc) can be seen. The minimal distance between the alveolar airspace (ai) and erythrocyte is about 800-900 nm. The endothelial nucleus is denoted as n. (B) Details of the lung alveolar epithelial and endothelial barriers. Numerous caveolae (arrows) are seen in the apical and basal plasma membranes of an ATI cell as well as endothelial cell (en) membranes. Caveolae may partake transport of some solutes (e.g., albumin). (C) ATII cells (ATII) are often localised in the comers of alveoli where septal walls branch off. (D) ATII cells are characterised by numerous multilamellar bodies (mlb) which contain components of surfactant. A mitochondrion is denoted as mi.

---