Respiratory System of Class 11
Alveoli are functional units of lungs.
They are lined by three types of cells
1. Type I Alveolar cells
2. Type II Alveolar cells
3. Dust cells
Type I Alveolar cells participate in exchange of gases and associate with the endothelial membrane of pulmonary capillaries and form Respiratory membrane through which exchange of gases takes place. This membrane is 0.25 mm thick and remains covered by surfactant. Surfactant is a mixture of phospholipids and reduce the surface tension during exchange of gases. It is secreted by Type II Alveolar cells.