DEV2022- LECTURE 9
Stages of lung development:
Embryonic: Very early on
Pseudoglandular: When the lung looks like a secretory gland
Canalicular: When canals and airways start becoming prominent
Saccular: When terminal sacs start to appear, which looks like gas exchange
Alveolar: When definitive alveoli mature
Birth normally occurs between the saccular and alveolar stage. The first three
stages always appear in vitro.
Premature babies can be born before the alveolar stage starts.
Stages of lung development before birth:
Surfactant is important for survival at birth. It is the soapy substance that lines
the alveoli, reduces the air liquid interface so we can expand the lung. Without
surfactant, the lung is almost not expandable. In humans, it starts to develop in
Embryonic stage of lung development:
Embryonic development starts at 4-7 weeks after conception. After 4 weeks, the
gut tube of the primitive gut (foregut endoderm, which is the primitive
esophagus) grooves into the anterior wall, and that groove goes deeper, so it
forms a pouch at the front, which is derived from the endoderm. It can be said
that the lung is developed from the gut.
Lung growth by dichotomous branching:
The lung grows by continual branching of a tube, which gives us incredible
complexity of the lung.
Branching morphogenesis is basically a tube dividing in two, and it's a very
complex procedure in a molecular sense. Primitive trachea branches to form
lobes or two branch points. Bronchial buds grow into the surrounding
mesenchyme (the tissue around them), and they continue to bud because of the
interaction b/w endodermal tissue and mesodermal tissue for this to take place.
Mechanisms involved in branching morphogenesis:
Mesenchymal cells is the cells that lungs grow in to. There are many molecules
involved in this process which are derived from the endoderm and mesoderm.
Epithelial buds bra