Embryology and Development of the Respiratory System

The respiratory system develops from the primitive foregut during embryogenesis. Initially, a respiratory diverticulum forms, which will eventually give rise to the trachea, bronchi, and lungs. The respiratory system primarily develops through branching morphogenesis, a process where the structures divide and expand. Epithelial-mesenchymal interactions during development play a crucial role in the differentiation and maturation of respiratory tissues. At around week 4 of development, the trachea undergoes longitudinal and lateral growth, leading to the formation of the main bronchi. By week 5, branching of the bronchi within the lungs begins, ultimately giving rise to the bronchial tree. The formation of respiratory bronchioles and alveoli occurs during late fetal development and continues postnatally. Cellular differentiation and maturation are tightly regulated by various signaling pathways, including those involving fibroblast growth factors and transforming growth factor-beta.