By:  Dr. Barb Goodman

    Cystic fibrosis is an inherited disease that is relatively common in the U.S.  Cystic fibrosis affects multiple parts of the body including the pancreas, the sweat glands, and the lungs.  When someone has cystic fibrosis, they often have lots of lung problems.  The cause of their lung problems is directly related to basic problems with diffusion and osmosis in the large airways of the lungs.
    People without cystic fibrosis have a small layer of salt water in the large airways of their lungs.  This layer of salt water is under the mucus layer which lines the airways.  The mucus layer in the airways helps to clear dust and other inhaled particles from the lungs.

    In people without cystic fibrosis, working cystic fibrosis proteins allow salt (chloride) to enter the air space and water follows by osmosis.  The mucus layer is dilute and not very sticky.


    In people with cystic fibrosis, non-working cystic fibrosis proteins mean no salt (chloride) enters the air space and water doesn't either.  The mucus layer is concentrated and very sticky.

  People with cystic fibrosis have lung problems because: 

    - Proteins for diffusion of salt into the airways don't work (less diffusion).
    - Less salt in the airways means less water in the airways (less osmosis).
    - Less water in the airways means mucus layer is very sticky (viscous).
    - Sticky mucus cannot be easily moved to clear particles from the lungs.
    - Sticky mucus traps bacteria and causes more lung infections.

    Therefore, because of less diffusion of salt and less osmosis of water, people with cystic fibrosis have too much sticky mucus in the airways of their lungs and get lots of lung infections. Thus, they are sick a lot. 

Created March 22, 2013
Center for Teaching and Learning