Development and developmental disorders of the respiratory system

ABSTRACT

Congenital anomalies of the respiratory system contribute significantly to respiratory stridor and other complications in neonates. They are often associated with abnormalities of other organ systems. The nasal placode deepens to form the nasal sac from which the nasal and olfactory mucosae develop. Paranasal air sinuses develop as extensions of the nasal cavity into the adjacent bony structures. Choanal atresia is probably a result of persistent oronasal membrane. The laryngotracheal primordium grows out from the ventral aspect of the pharyngeal portion of the foregut during week 4 of embryonic life. The larynx and trachea represent the proximal portions of this endodermal outgrowth. The lung buds arise from the tip of this outgrowth. The laryngeal cartilages and muscles develop from the 4th and 6th pharyngeal arches. Posterior laryngeal clefts might involve the interarytenoid fold, cricoid lamina or the posterior wall of the entire larynx and trachea. Laryngomalacia resulting from abnormal development of laryngeal cartilages causes respiratory stridor in pediatric patients. Laryngeal webs, stenosis and atresia are possibly recanalization defects and are the anatomical basis of congenital high airway obstruction syndrome. Defective neural crest development appears to be the common denominator between obstructive lesions of the upper airway and several craniofacial malformations. The lung bud branches dichotomously and constitutes the bronchial tree. There is a morphogenetic tissue interaction between the endodermal epithelium and the surrounding mesenchyme during lung development. Branching morphogenesis appears to be guided by FGF, SHH, BMP-4, and Gli2, Gli 3 signaling. SFTPB, SFTPC and ABCA3 genes have been found to control surfactant production. Molecular and cellular bases of the development and developmental control mechanisms of the respiratory tract are only beginning to be understood