ANAT 1625 Embryology of the Lungs

ANAT 1625 Embryology of the Lungs - Mature alveoli continue...

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Embryology of the lungs The respiratory system develops from two germ layers. The epithelia lining arises from the endoderm, which forms the lining of the foregut. A small diverticulum buds off the ventral surface of the foregut to form the lung bud. This grows into the splanchnopluric mesoderm, enlarging and buldging into the future pericardioperitoneal canals. These two components of the intraembryonic coelom become the pleural cavities. The lung buds divide rapidly by a process known as branching morphogenesis regulated by a variety of molecular signals. There is however, an asymmetry in this division such that the left lung has two lobes and the right has three. The cartilage and smooth muscle of the airways and visceral pleura develop from the surrounding splanchnopluric mesoderm. The samatopleuric mesoderm lines the future thoracic wall, as parietal pleura.
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Unformatted text preview: Mature alveoli continue to develop until 6 or 7 years of age. Lung development passes through a number of phases: from an initial glandular stage to a tubular phase resulting in formation of the airway tubes. After 26 weeks of fetal life the lining of the alveoli thins from a cuboidal to a simple squamous epithelium, thereby facilitating gaseous exchange. It is not until after this time that air breathing is possible and is a reason why premature infants younger than 26 weeks are often non-viable. Type I alveolar cells line the walls of the alveoli; Type II alveolar cells produce surfactant, a phospholipid material which reduces the surface tension of the fluid in the lungs, This helps prevent collapse of the alveolar spaces. Infants in whom type II alveolar cells do not produce surfactant may suffer from respiratory distress syndrome....
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