Curriculum Module
Respiratory System Development
The respiratory system begins developing in the 4th week. It is anatomically divided into an Upper Respiratory Tract (nose, nasal cavity, paranasal sinuses, laryngopharynx, larynx) and a Lower Respiratory Tract (trachea, primary bronchi, lungs), developing primarily from the endoderm (lining) and splanchnic mesoderm (cartilage and muscle).
Embryonic Origins & Lung Buds
The respiratory system develops from two primary structures: the Endoderm which forms the epithelial lining and glands, and the Splanchnic Mesoderm which forms cartilage, smooth muscle, and connective tissue. Emerging exclusively from the Foregut, the system forms as the embryo folds.
At around 4 weeks, a Respiratory Diverticulum (Lung Bud) appears, dependent on a Retinoic Acid increase produced by the adjacent mesoderm. It maintains communication with the pharynx through the laryngeal orifice. As it grows caudally, tracheoesophageal ridges form and fuse, creating the Tracheoesophageal Septum.
Key Insight
This stage is critical for the formation of embryonic support structures, establishing the main body axis.