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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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- Winter '11