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Lung Embryology (Segmental branching and development of bronchial tree…

- - - - Dilated pocket appear as empty cysts in XR
- - - - growth of pleuroperitoneal membrane from the lateral body towards the septum transversum closes the canal
      - Disruptions are a frequent cause of congenital diaphragmatic hernias (CDH)
      - usually are at the aortic or esophageal hiatus, where the diaphragm stops to allow passage of these through, and are usually minor as size is small
      - CDH rarely occurs at the right due to liver being in the way
      - Normally happens on the left, large defect allowing intestine to herniate into the left pleural cavity, interfering with development of the left lung and in some cases, causing agenesis of the left lung
- - - - Act as a pro-inflammatory agent on macrophages present in amniotic fluid.
      - Activated macrophages invade uterine wall, begin releasing interleukin-1beta (?), which ultimately leads to localized prostaglandin production that stimulates uterine smooth muscle to contract
    - - Respiratory Distress Syndrome (RDS) or Hyaline Membrane Disease ocurs when there is inadequate surfactant, either due to deficiency or inadequate production by type II pneumocytes
      - airways collapse (or under inflated), become inflamed, result in deposition of a glassy, proteinaceous film (hyaline membrane) on alveolar surface that impedes gaseous exchange (thick and fibrotic)
      - In infants: type II pneumocytes havent developed enough
      - Another factor is prolonged intrauterine asphyxia/hypoxia
        Maternal smoking, compromised cardiorespiratory function in mother, or mechanical obstruction of uterine arteries such as impinging tmor
- - - - Disruption of mesoderm, retinoic acid or TBX4 expression in endoderm will interfere with this process and cause defects in lung/trachea development
    - - Disruption can cause tracheo-esophageal fistulas
      - Associated with VACTERL
      - Most common: proximal esophagus ends blindly whereas distal esophagus communicates with trachea via a fistula
        
        Prental: polyhydraminos due to inability of fetus to swallow and recycle the amniotic fluid
        
        Postnatal: infants cough and choke immediately upon feeding due to inability to swallow
        gastric contents get into lungs, causing irritation and possibly pneumonitis
        
        Extreme example is trachea atresia, where trachea fails to form entirely and lungs bud directly from esophagus