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Pulmonary Host Defence - Dr Sunil Sharma Senior Resident...

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Dr Sunil Sharma Senior Resident Dept. of Pulmonary Medicine
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` major function of the respiratory system is to major function of the respiratory system is to procure O 2 & to eliminate CO 2 from the body at rates required by tissue metabolism ` Ambient inspired air along with O contains Ambient inspired air along with O 2 contains noxious gases and a multitude of particulates including viable microorganisms Toxic substances in air are derived from ` Toxic substances in air are derived from many sources
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` naturally occurring processes can give rise to naturally occurring processes can give rise to large amounts of aerosolized particles including resuspension of soil emissions from volcanic activity forest fires, photochemical reactions etc. Ai b i l l i l d bi l i ll ` Airborne particles also include biologically derived viruses, bacteria, fungi, algae, spores, and pollens ` Industrial and occupational sources add SO 2 , CO NO NH O hydrocarbons & inorganic and CO,NO 2 , NH 4 ,O 3, hydrocarbons & inorganic and organic particles to the inspired air
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` Upper and lower airways represent the largest Upper and lower airways represent the largest epithelial surface exposed to the outside environment ` Size of alveolar surface is that of a tennis court ` To allow gas exchange foreign substances and microorganisms must be stopped and removed without inducing inflammation ` variety of defences exists to protect host from the harmful effect of microorganisms & air pollutants
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Airways and their mucosa ` Luminal defence mechanisms Anatomical barrier Cough Mucociliary clearance ` Blood derived cells of the mucosa Dendritic cells Lymphocytes (T-cells; cd; NK cells) Secretory IgA Lysozymes, lactoferrins Defensins Epithelial cells B lymphocytes Eosinophils; mast cells; basophils ` Epithelial barrier Mucin release Antimicrobial peptides Alveolar spaces ` Pneumocyte types I and II Alveolar macrophages Bacterial receptors Chemotactic factors Growth factors; cytokines ` ` Lymphocytes ` Neutrophils ` IgG and opsonins ` Surfactant
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Anatomical barrier ` nose is efficient upper airway defence mechanism that removes most airborne particles and water- soluble gases from inspired air ` Air entrained through the nasopharynx is subject to filtration through tortuous epithelial passages ` foreign particles of 10 μ m effective diameter are ffi i tl d & l h i i t i t i efficiently removed & nasal hairs assist in trapping larger inhalants ` sneezing is an effective means of expelling some of airborne contaminants
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` Microbes deposited into & attempting to colonize the Microbes deposited into & attempting to colonize the nasopharynx has to compete against a dense flora of nonpathogenic endogenous bacteria ` Ciliated mucosal lining of the posterior nasopharynx propels mucus and trapped foreign material into the propels mucus and trapped foreign material into the oropharynx b i b i d i h li d h ` bacteria become mixed with saliva and are then swallowed or expectorated ` Anatomic barriers of the epiglottis and vocal cords make aspiration into the trachea physically difficult
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