Final answer:
Embryonic development of the respiratory system begins around the fourth week with the formation of the olfactory pits and the lung bud from ectodermal and endodermal tissues, respectively.
Step-by-step explanation:
Development of the Laryngopharynx and Lung Bud
During the embryonic development of the human respiratory system, a series of complex processes take place to form the various structures involved in breathing and gas exchange. Around week 4, respiratory development starts with the formation of olfactory pits from ectodermal tissue, which eventually become part of the nasal cavity. Concurrently, the lung bud appears, a dome-shaped structure bulging from the endoderm of the foregut situated just inferior to the pharyngeal pouches. This bud elongates longitudinally to form the laryngotracheal bud, which will give rise to the trachea near the pharynx and bronchial buds at the distal end.
The laryngopharynx, positioned inferentially to the oropharynx and posterior to the larynx, acts as a conduit for both ingested material and air. The epithelium of the oropharynx is continuous with that of the laryngopharynx. Anteriorly, the laryngopharynx opens into the larynx, connecting to the respiratory tract, while posteriorly, it enters the esophagus, leading to the digestive system.
During these developmental stages, the structures necessary for the crucial functions of the respiratory system take shape. The trachea forms at the proximal end of the laryngotracheal bud while the distal end forms the bronchial buds, which will become the bronchi and later expand to form the full complexity of the lower respiratory system.