Thorax

■ The respiratory system (Fig. 16.1) arises as an out-pouching from the primitive lung bud at the 3rd week of embryonic life. Between the 6th and 16th weeks of gestation, rapid bronchial division beyond the subsegmental level occurs ■ Alveoli begin to develop at the 24th week of gestation by out-pouching, so that by 8 years of age the adult number of approximately 300 million alveoli is attained ■ Each lung is divided into 10 segments (Fig. 16.2). For certain localized lesions segmental and subsegmental resections rather than lobectomy should be performed ■ The pulmonary lymph nodes are located at points of division of segmental bronchi or at the bifurcations of the pulmonary artery. The hilar nodes are allocated along the main bronchi. The interlobar nodes are situated in the angles of the main bronchi into the lobar bronchi ■ The child’s thorax is more flexible than that of adults