ABSTRACT

This chapter describes the embryology, anatomy, and histology of the respiratory system. The respiratory system allows gas exchanges between ambient air and blood circulation by extracting oxygen from inhaled air into blood and rejecting carbon dioxide from the blood into exhaled air. The lungs do not perform a respiratory function during intrauterine life. Instead, they are responsible for the production of amniotic fluid. From the 6th to the 16th gestational weeks, the entire conducting airways are formed by a succession of ramifications culminating in the terminal bronchioles. During the last weeks of pregnancy, new alveolar sacs continue to form, eventually leading to their final and smallest subdivisions, the alveoli. The average weight of the two lungs is 850 g in men and 750 g in women. The lungs have a dual blood supply: pulmonary and systemic. Each pulmonary lobule is delimited by the pleura and/or interlobular septa.