A pair of lung buds forms at E9.5. During the embryonic stage (up to week 7 of gestation in humans), the lung bud appears as a ventral diverticulum of the foregut and divides within the surrounding mesenchyme to form the left and right lung. Once the primary lung buds have formed, they extend into the surrounding mesenchyme and begin the process of branching morphogenesis.
The lung buds consist of three cell layers: the inner epithelium (endodermal origin), which is surrounded by loosely packed mesenchyme and a thin outer mesothelial (squamous epithelial) layer. No bud extension occurs in mutants lacking FGF10, although the trachea does separate.
Multiple AncestorsSingle AncestorNo DescendantsDevelops fromPart of Parent