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Lecture 9

DEV2022: Lecture 9 notes

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Monash University

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 surfaces 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 late gestation. 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: 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. Pseudoglandular stage: Epithelial buds bra
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