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what are the two main functions of surfactant in the lungs?
- decrease the surface tension of alveolar epithelium - easier to expand during inflation, prevents collaps during deflation
- hydrophobic barrier between air and alveolar cells - keeps fluid in and air space intruders out
what happens if mucus is hypersecreted in conducting airways?
- cough and production of sputum
- plugging of airways, gas trapping, reduced gas exchange
what is mucus secreted by?
submucosal glands and goblet cells
what are the three functions of mucus?
- protecting respiratory epithelium
- entrapping inhaled particles and microorganisms
- providing anti-inflammatory, antibacterial, and antioxidant substances
what are the two layers of mucus and their functions?
- sol-layer: allows free movement of the cilia (low viscosity)
- gel-layer: (on top of sol-layer and cilia, high viscosity) traps particulate matter
where would you find a high concentration of CFTR?
secretory organs (pancreas, sweat glands, reproductive glands)
what are four important functions of clara cells?
- unciliated secretory cells
- precusors of ciliated cells
- primary site of airborne xenoblotic metabolism
- synthesis and secretion of proteins involved in immune defense (IgA)
what is the primary function of type I alveolar cells?
gas exchange (surface of alveolar)
what is the major function of type II alveolar cells?
what is the surfactant layer of the alveolar lumen composed of?
- 90% phospholipids, half of wich is dipalmitoyl-phosphatidylcholine (DPPC)
- 10% surfactant proteins
when does the synthesis of surfactant from type II alveolar cells begin?
24 weeks in utero and continues for life
what are the 7 steps of pulmonary surfactant synthesis in type II alveolar cells?
- 1. surfactant components synthesized - lipids on smooth ER, proteins on rough ER
- 2. golgi complex modifies and secretory vesicle form lamellar bodies
- 3. contents of lamellar bodies secreted by exocytosis, constitutive secretion but can be increased by mechanical stimuli (deepened respiration
- 4. surfactant unfolds to form tubular myelin (TM)
- 5. surfactant is integraded into the expanded surface monolayer during inhalation
- 6. surfactant is compressed forming closely packed monolayer of DPPC during exhalation
- 7. excluded material forms small aggregates which are endocytosed by alveolar macrophages (8) or endocytosed and recycled by type II alveolar cells
what is the function of surfactant proteins SP-A and SP-D?
- formation of lamellar bodies
- regulate secretion and re-absorption of surfactant phospholipids
- stimulate immune response by binding to microorganisms and promoting their phagocytosis by macrophages
- (they are hydrophilic poteins)
what is the function of surfactant proteins SP-B and SP-C?
- inserting phospholipids into the surfactant monolayer
- promote spreading of surfactant lipids
- (they are hydrophobic membrane proteins)
what is the function of surfactant proteins SP-A and SP-B?
required for formation of tubular myelin
what test is used to predict lung maturity and the risk of NRDS?
- amniocentesis to determine the PC/SM ratio (phophatidylcholine/sphingomyelin)
- PC/SM less than 2 suggests immature ling and elevated risk of RDS
- also, and immunoassay for SP-A can be used
what is given to mothers at risk for pre-term delivery when the PM/SM ratio is low?
glucocorticoid (stimulates type II cells to produce surfactant by increasing surfactant synthesis)
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