Spencer's Pathology of the Lung: The normal lung: histology, embryology, development, aging and function

Introduction Knowledge of normal lung anatomy and function is important for the interpretation of lung biopsies and resections. An understanding of different cell structures and functions allows for a greater appreciation of disease states. In addition basic pulmonary embryology explains congenital pulmonary defects. At the other extreme of life, knowledge of how the lung ages is important, not only for consideration of other diseases, such as hiatus hernias with co-existent aspiration, but also because of the world's increasing elderly population. Development The key events of pulmonary embryogenesis and postnatal development are discussed in this chapter. For a more detailed account, the reader is referred to two monographs and several review articles. The events of human lung growth are divided into five continuous stages, based on anatomic and histological characteristics. These are the embryonic, pseudoglandular, canalicular, saccular and alveolar stages (Table 1) (Figures 1 and 2). Airway and vascular development are closely related. The conducting airways are formed in the embryonic and pseudoglandular stages, while gas exchange units characterized by vascularization and reduction of mesenchyme are formed in the canalicular, saccular and alveolar stages.