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Updated: Jun 5 2018

Important Lung Products

  • Surfactant
    • Alveolar Surface Tension
      • surface tension generates a pressure that tends to collapse alveolus
      • law of Laplace
        • P = 2T/r
          • P = collapsing pressure on alveolus = pressure required to keep alveolus open
          • T = surface tension
          • r = radius of alveolus
        • pressure tending to collapse alveolus is directly proportional to surface tension generated by molecules of liquid lining alveolus (gas-liquid interface)
        • pressure tending to collapse alveolus is indirectly proportional to alveolar radius
          • large alveolus (large radius) has a low collapsing pressure
          • small alveolus (small radius) has a high collapsing pressure
          • surface tension → tendency for alveolar collapse on expiration
            • expiration → ↓ alveolar radius
    • Surfactant
      • a mixture of phospholipids that line alveoli and reduce alveolar surface tension
        • consists primarily of dipalmitoyl phosphatidylcholine (DPPC), or lecithin
      • synthesized by type II pneumocytes
      • ↓ alveolar surface tension → ↓ collapsing pressure on alveolus
        • small alveolus remains open
      • ↑ lung compliance → ↓ work of expanding lungs during inspiration
        • without surfactant, small alveolus has a tendency to collapse (atelectasis)
    • Neonatal Respiratory Distress Syndrome (RDS)
      • caused by a deficiency or absence of surfactant
        • ↑ surface tension → ↑ collapsing pressure on alveolus → alveolar collapse
          • → ↓ V/Q
            • collapsed alveoli are not ventilated and do not participate in gas exchange
            • → hypoxemia
        • ↓ lung compliance → ↑ work of expanding lungs during inspiration
          • difficulty reinflating lungs
  • Additional Important Lung Products
    • Prostaglandins
    • Histamine
      • binds receptors on smooth muscle cells
        • induces vasodilation, bronchoconstriction
    • Kallikrein
      • catalyzes proteolytic cleavage of kininogens in kinin synthesis
        • inactive kininogens → active kinins (e.g., bradykinin)
      • e.g., bradykinin binds receptors on endothelial cells
        • induces vasodilation, bronchoconstriction
    • Angiotensin-Converting Enzyme (ACE)
      • catalyzes angiotensin I → angiotensin II
        • angiotensin II induces vasoconstriction
      • acts as a kininase in kinin degradation
        • ACE inactivates bradykinin
        • ACE inhibitors → ↑ bradykinin → cough, angioedema
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