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Surfactant, biosynthesis and its regulation

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Surfactant, biosynthesis and its regulation

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Surfactant, biosynthesis and its regulation

  1. 1. SURFACTANT, BIOSYNTHESIS AND ITS REGULATION Prepared by Nixon Dangol Janaki Medical College and Teaching Hospital, 11th batch
  2. 2. What is Surfactant? • These are amphiphilic compounds that reduces the surface tension of fluid. • It acts by adsorption into the liquid surface. The water-insoluble hydrophobic group extends out of the bulk water phase into the air, while the water-soluble head group remains in the water phase. This reduces the surface tension of the liquid.
  3. 3. Pulmonary Surfactant • It is the surfactant that lines the alveolar epithelium. It reduces the surface tension of water/fluid in alveolar membrane. • It prevents the collapsing of alveoli (pneumothorax) and stabilizes alveolar size and total lung volume. • Reduction of surface tension also reduces the oncotic pressure of alveoli that checks the pulmonary edema.
  4. 4. Pulmonary surfactant composition
  5. 5. Biosynthesis of Surfactant Type II epithelial cells synthesize and assemble the lipid and protein components into complexes that are stored as tightly packed membranes in lamellar bodies until secreted into the alveolar airspace Lamellar Body Maturation The alveolar epithelial cell surface is covered by a thin aqueous layer (hypophase) in which newly secreted, tightly packed surfactant membranes reorganize to form a loose network of interconnected membranes that contacts the air-liquid interface.
  6. 6. unraveling of secreted lamellar bodies to form intermediate structures such as tubular myelin (TM) or large surfactant layers that have the potential to move and transfer large amounts of material to the interface, and rapid movement of surface active species through a continuous network of surfactant membranes, a so-called surface phase, connecting secreting cells with the interface. hydration of surfactant complexes, pH, or calcium concentration
  7. 7. Regulation of Surfactant • Surfactant secretion is regulated locally in the lung by changes in ventilation rate, possibly mediated by distension and altered intracellular pH. • SP-A and dipalmitoylphosphatidylcholine, can inhibit secretion in vitro, but the mechanism is not known. • Compression-expansion cycling leads to progressive conversion of the surface active fractions of surfactant into much less active lipid/protein complexes. The alveolar surfactant pool is continuously depleted through cellular uptake by type II epithelial cells and alveolar macrophages as well as removal via the mucociliary escalator. It maintains Surfactant Recycling and Surfactant Homeostasis.

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