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HBIO1 > Cystic Fibrosis
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Cystic Fibrosis

  • Caused by a mutation of the Cystic Fibrosis Transmembrane Regulator (CFTR) gene
    • Covered in Unit 2 Section 3.2.1
  • CFTR is a plasma membrane protein
    • Normally, it transports chloride ions out of the cell by active transport
    • In cystic fibrosis, a mutation alters the tertiary structure of CFTR
    • The protein fails to reach plasma membrane
    • Accumulation of Cl- and Na+ (attracted by negative Cl-) within the cell
    • Secretions are thick as water stays inside the cell due to high internal Na+ (altered water potential)
    • NB: water always follows Na+
  • Lungs
    • "Produce less mucus than normal "1
    • Lung surface is dehydrated and mucus adheres to airways
    • This favours the growth of bacteria causing chronic infection
    • White cells engulf bacteria and die (phagocytosis)
    • The DNA from dead inflammatory cells (pus) contributes to thick sputum
    • Sputum has an increased viscosity and cannot be removed by the ciliary escalator
    • Obstructs airways and causes further inflammation
  • Pancreas
    • Thick digestive juice blocks passage from pancreas into small intestine (duodenum)
    • Obstruction may cause chronic inflammation of the pancreas
    • Pancreas fails to secrete digestive enzymes
    • Food is not broken down and not absorbed
  • Sweat
    • CFTR works differently in the skin
    • Normally, chloride are transferred from the sweat into the cell
    • Excessive NaCl remains on the skin - sweat taste saltier than normal
    • Sweat can be collected and analysed to diagnose CF
  • Slow growth
    • Less efficient energy/fooduptake due to malabsorption
    • High energy consumption due to chronic inflammation of the lungs
    • To compensate, children require high calorie diet (chocolate, crisps)
  • Treatment
    • Pancreatic enzyme replacement therapy (PERT) to treat fat malabsorption
    • Fat-soluble vitamin supplements (A, E, D, K) to prevent deficiencies
    • Inhaled enzyme DNAse breaks down excessive DNA and thin mucus
    • Antibiotics to treat lung infections (frequent use causes antibiotics resistance)
References
  • 1) Henke MO, Renner A, Huber RM, Seeds MC, Rubin BK. MUC5AC and MUC5B Mucins Are Decreased in Cystic Fibrosis Airway Secretions. Am J Respir Cell Mol Biol. 2004 Jul;31(1):86-91. Epub 2004 Feb 26.