5. Fate after pulmonary administration

5.1 Lung physiology

The role of the lung is to oxygenate the blood by bringing oxygen from the air and eliminating carbon dioxide. The channels carrying these gases are the bronchi and bronchioles. The pulmonary tree comprises 23 bifurcations, leading from the larger bronchi to the bronchioles and on to the pulmonary alveoli, where gas exchange takes place. At the proximal level, the epithelium is pseudostratified and composed of waxy cells and mucus-secreting caliciform cells. The epithelium then thins to become very thin at the level of the pulmonary alveoli. It is then composed of two cell types: type I pneumocytes (95% of cells) and type II pneumocytes, which produce surfactant and are the precursors of type I pneumocytes. Surfactant is a substance that forms a film over the...