SURFACTANT - SURFACTANT IN HEALTH AND DISEASE DR. AMIT...

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1 SURFACTANT IN HEALTH AND DISEASE DR. AMIT RAODEO INTRODUCTION ¾ Lung epithelium is in close contact with environment-acts as barrier. ¾ Appropriate balance between pro and anti inflammatory response is critical. ¾ Airspace lined with a lipoprotein complex called surfactant – named so because of its ability to reduce surface tension . ¾ Also plays important role in host defense mechanism. ¾ SP-A and SP-D,members of collectin family-involved in innate immunity.
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2 COMPOSITION AND SYNTHESIS COMPOSITION AND SYNTHESIS ¾ All components synthesised by Type II alveolar cells. ¾ Surfactant complex released from intracellular storage granule, the lamellar body into liquid hypophase that covers alveolar epithelium. ¾ Lamellar body is then transformed into lattice like structure called tubular myelin. ¾ Monomolecular film which reduces surface tension is formed at air liquid interface. ¾ Composition of this film is mostly of Dipalmitoylphosphatidylcholine(DPPC).
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3 METABOLISM ¾ Major pathway – ¾ 1)uptake by TYPE II cells where both recycling and degradation occurs. 2) significant fraction is degraded by alveolar macrophages. ¾ Minor pathway-movement up the airway and across epithelial- endothelial barrier. Surfactant Proteins ¾ These are SP-A,SP-B,SP-C and SP-D. ¾ All except SP-C are synthesised by clara cells of airway. ¾ SP-B and SP-C are highly hydrophobic and facilitate adsorption of lipids to an air- liquid interface. ¾ SP-A and SP-D are relative hydrophilic and does not contribute to surface reducing property. ¾ SP-D binds to phosphatidylinositol which is minor component in surfactant isolates. ¾ The levels are elevated and ratio with phosphatidylglycerol is reversed in disease states like PAP,IPF,ARDS.
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4 CELLS INVOLVED IN PULMONARY HOST DEFENSE A) Alveolar Macrophages: ¾ Most abundant component of BAL fluid (85%). ¾ Primary defender of alveolus from infection. ¾ Role was recognised in 1967 by Green and co- workers. ¾ Surfactant proteins have been shown to regulate variety of macrophage function. CELLS INVOLVED IN PULMONARY HOST DEFENSE (CONTD) B) PMN leucocytes: ¾ Major cells implicated in variety of noninfectious diseases including IPF, asthma and emphysema and variety of infectious disorder. ¾ Comprise of 1-3% of cells in BAL fluid. ¾ Also play important role in ARDS. ¾ Surfactant inactivation secondary to influx of serum protein is important manifestation of disease leading to increased surface tension and reduced compliance.
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5 CELLS INVOLVED IN PULMONARY HOST DEFENSE (CONTD) D) Alveolar type II cells: ¾ Not a traditional immune cell but studies have shown that it may have immunoregulatory function. ¾ In addition to surfactant, complement components like C2,C3,C4,C5 and factor B are secreted by these cells. ¾
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SURFACTANT - SURFACTANT IN HEALTH AND DISEASE DR. AMIT...

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