Alveoli are the exchange surface in the lungs, where oxygen from inhaled air moves into the blood, and carbon dioxide moves out of capillaries into the air. Alveoli are capillary-rich, thin-walled sacs, that create an optimum surface for gas exchange. There are two types of alveolar cell, type I and type II. Type I alveolar cells are for gas exchange, type II cells synthesise and secrete surfactant. In type I cells the alveolar epithelium and capillary epithelium are fused by a basement membrane.
- ↑ Silverthorn D (2010). Human Physiology: An Integrated Approach. 5th ed. San Francisco: Pearson Benjamin Cummings. 570-575