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Introduction to Respiratory System



Five periods-

  1. Embryonic period - begins at 4 weekQ
    2 stem bronchial buds
  2. Pseudoglandular period (6th week to 16 week) Q
    The trachea and the foregut are separated after the progressive fusion of epithelial ridges.
    1. Incomplete fusion of these ridges results - Tracheo-esophageal fistula.
    2. Incomplete fusion - Congenital diaphragmatic hernia of Bochdalek most commonly on left side.
  3. Canalicular period (16th  and 26-28th week) Q
    1. ​Type II pneumocytes
  4. Saccular period (26-28 week)Q
  5. Alveolar period
    1. Thyroid hormone - stimulates septations
    2. Glucocorticoids

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