ANATOMY

Detailed explanation-1: -When the embryo is approximately 4 weeks old, the respiratory diverticulum (lung bud) appears as an outgrowth from the ventral wall of the foregut. The appearance and location of the lung bud are dependent upon an increase in retinoic acid (RA) produced by adjacent mesoderm.

Detailed explanation-2: -At the beginning of the 4th week, during the development of the respiratory system, the laryngotracheal notch is the first to appear from the ventral side of the foregut.

Detailed explanation-3: -The respiratory diverticulum appears on the ventral wall of the primitive foregut endoderm, posterior to the pharynx. The ventral wall rostral to the lung buds now pinches off from the dorsal wall to form a parallel tube which, after caudal elongation, forms the trachea anteriorly and the esophagus posteriorly.

Detailed explanation-4: -While fetal lung development consists in the pseudoglandular, canalicular and saccular stages, postnatal lung development comprises the stages of classical and continued alveolarization, as well as of microvascular maturation.

Detailed explanation-5: -The lung bud sometimes referred to as the respiratory bud forms from the respiratory diverticulum, an embryological endodermal structure that develops into the respiratory tract organs such as the larynx, trachea, bronchi and lungs. It arises from part of the laryngotracheal tube.