Comprehensive knowledge of the anatomy and physiology of the respiratory system is crucial in respiratory medicine. A profound understanding of physiology allows the practitioner to deduce pathological processes and initiate therapeutic steps based on rational decisions. The choice of a suitable ventilation mode or setting typically stems from an understanding of the pathophysiological processes. Understanding the respiratory chain at the cellular level, ventilation and perfusion, as well as the delicate interplay of macroscopic and microscopic mechanisms, supports the development of precise and individualized ventilation strategies. Knowledge of mucociliary clearance and the various lung volumes is also crucial to ensure optimal management of tracheobronchial secretions, oxygen supply and CO2 elimination.