<prompt> True regarding physiology of surfactant isSP-A SP- D are hydrophobic SP-B SP- D are hydrophilicSecreted into alveolar lumen as tubular myelinSP-A plays a major role in innate host defense of the lungPulmonary surfactant is composed of 80 lipids and 20 proteins.  <response>: Answer: c SP-A plays a major role in innate host defense of the lungSURFACTANT Produced by type-ll alveolar cellsgranular pneumocytes Synthesis and storage of surfactant begins at about 16 weeks of gestation, and lung homogenate: have high concentrations of surfactant by 20 weeks. However, surfactant is not secreted until later, appearing in amniotic fluid between 28 and 38 weeks of gestation. Starts at 28 weeks of gestation peaks at 35weeks The lamellar inclusion bodies in type-ll cells store surfactant. Lamellar inclusion bodies are continuously discharged into the alveolar surface by constitutive exocytosis. Lamellar inclusion body materials are converted to tubular myelin, which forms the surfactant layer. Composition:o Pulmonary surfactant is a complex mixture of phospholipids, neutral lipids, fatty acids, and proteins.o 85 to 90 lipids, predominantly phospholipids: Major phospholipid is phosphatidylcholine, approximately 75 of which is present as dipalmitoyl phosphatidylcholine DPPC Second most abundant phospholipid is phosphatidylglycerol PGo 10 to 15 proteins. Functions: -o Reduces alveolar surface tension surface tension is inversely proportional to the surfactant concentration per unit areao Prevent alveolar collapseo Prevents pulmonary edema Surfactant proteins are SP-A, SP-B, SP-C, and SP-D. SP-A: large glycoprotein regulates the feedback uptake of surfactant by the type II alveolar cells. SP-B and SP-C: hydrophobic, facilitates formation of the monomolecular film of phospholipid. Mutation of SP-C -familial interstitial lung disease. SP-A and SP-D: members of collectin family, involved in innate immunity in the conducting airway as well as in the alveoli. Synthesis of surfactant is facilitated by:o Glucocorticoidso Thyroxineo Insulino Stretching of lungs in infancy yawning sighingo Beta agonistso Calciumo Regular exercise Deficient conditions: occlusion of main bronchuspulmonary artery, smoking, long term inhalation of 100 oxygen Deficiency causes: IRDS Hyaline membrane disease In 1959, Avery and Mead discovered it, patchy atelectasis ARDS Over production or dysregulation of surfactant synthesis lead to respiratory distress is the cause for pulmonary alveolar proteinosis Surface tension of:o Pure water, 72 dynescm;o Normal fluids lining the alveoli without surfactant: 50 dynescm;o Normal fluids lining the alveoli with normal amounts of surfactant: between 5 and 30 dynescm. 