What is the main origin of respiratory system?

The main origin of the respiratory system is from the endoderm, specifically from the ventral foregut. The foregut is the most anterior part of the primitive gut, and it develops into the respiratory and digestive systems. The respiratory system arises from the ventral foregut, which gives rise to the trachea, bronchi, and lungs. During embryonic development, the endodermal cells of the foregut thicken and form a respiratory diverticulum, which evaginates and develops into the respiratory system.