12/24/2023 0 Comments If the bronchioles in the lungs are dilated the anatomic dead space course heroBeyond the vestibule, the nasal passages are lined by pseudostratified ciliated columnar epithelium ("respiratory epithelium"). NoseĪir inhaled through the nostrils is warmed and filtered in the vestibule lined by stratified squamous epithelium. Alveolar type II cells become more numerous, but actual fetal lung maturity with enough surfactant to survive extrauterine life without serious complications is reached between 34 and 36 weeks gestation. Beyond 26 weeks, there is continued branching with formation of alveoli, and this is the saccular phase of development. From 23 to 25 weeks gestation on, there is enough lung to survive (barely) if birth occurs, supported by mechanical ventilation. This is the canalicular phase of development. From 16 weeks to 26 weeks gestation, the bronchioles begin to give rise to more complex structure with branching to respiratory bronchioles and alveolar ducts. There is so little surface area for gas exchange through thick bronchioles that survival is not possible if birth occurs. Under 16 weeks gestational age, a histologic section of lung parenchyma will reveal mainly small round bronchioles, and this stage is known as the tubular (glandular) phase of development. The most prominent structures early on are the bronchi and bronchioles. Continued cell division produces greater volume of the lungs. In early fetal life, the lungs bud off the esophagus and form a connection with the trachea to the oropharynx. Respiratory Tract and Lungs Respiratory Tract and Lungs Return to the Histology Tutorial menu.
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