5. Becoming after pulmonary administration

5.1 Physiological reminders of the lung

The role of the lungs is to oxygenate the blood by supplying it with oxygen from the air and allowing it to eliminate carbon dioxide. The channels that transport these gases are the bronchi, followed by the bronchioles. The pulmonary tree has 23 branches, leading from the largest bronchi to the bronchioles and finally to the pulmonary alveoli, where gas exchange takes place. Proximally, the epithelium is pseudostratified and composed of ciliated cells and goblet cells that secrete mucus. The epithelium then becomes thinner and very fine 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....