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Pathophysiology

Pathophysiology. Fetal Lung Development. Sequence of Events During Birth. External compression of the thorax ejects some of the amniotic fluid from the lungs recoil of the chest wall. Facilitates the first active inspiratory movement entry of air into the lungs

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Pathophysiology

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  1. Pathophysiology

  2. Fetal Lung Development

  3. Sequence of Events During Birth • External compression of the thorax • ejects some of the amniotic fluid from the lungs • recoil of the chest wall. • Facilitates the first active inspiratory movement • entry of air into the lungs • inflates the alveoli • Amniotic fluid is exhaled and resorbed • Alveoli is coated with surfactant • Decreases the external compression of the capillaries in the alveolar walls • Pulmonary blood flow suddenly rises

  4. Sequence of Events During Birth • Dilatation of arteries and arterioles • Due to increased alveolar oxygen tension • Causing expansion of precapillary vascular space • Absorption of alveolar fluid • Decreased vascular pressure in the entire pulmonary circulation • influx of blood from the right ventricle • Resulting in increased lymph flow and flow of oxygenated blood into the LA • Closure of the ductusarteriosus • Transformation of the fetal high-resistance, low-flow pulmonary circulation into the adult low-resistance, high-flow circulation

  5. Surface Tension & Surfactant • Internal surface of the alveolus is covered with a thin coating of fluid • Water in this fluid has a high surface tension which promotes collapse the alveolus • Pulmonary surfactants decrease surface tension of water • Increases lung compliance • Prevents collapse of alveoli during expiration

  6. Surfactant Metabolism

  7. Pulmonary Surfactants • 70-80% phospholipids • Phosphatidylcholine (76%) - lecithin • Phosphatidylglycerol (13%) • Phosphatidylinositol (4%) • Phosphatidylethanolamine (3%) • Sphingomyelin (2%) • Other phospholipids (2%) • 8-10% protein (apoproteins) • 10% neutral lipids, primarily cholesterol

  8. Surfactant Apoprotein • SP-B and SP-C • small hydrophobic proteins that comprise 2-4% of the surfactant mass • present in commercially available surfactant preparations • facilitate rapid adsorption and spreading of DPPC as a monolayer to lower the surface tension at the alveolar air-fluid interface in vivo during expiration, thus preventing atelectasis • SP-A • innate host defense, large molecular, hydrophobic protein that regulates lung inflammation • facilitates phagocytosis of pathogens by macrophages and their clearance from the airways • SP-D • also binds pathogens and facilitates their clearance

  9. Respiratory Distress Syndrome • Also known as hyaline membrane disease • Caused by a deficiency in pulmonary surfactant • Most common cause of respiratory failure in neonates • Incidence is indirectly proportional to gestational age at delivery

  10. Pathophysiologyof RDS

  11. Microscopic appearance of lungs of an infant with respiratory distress syndrome

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