Learn About Your Lungs

How the Respiratory System Works 


The respiratory system has two main parts:

  • Upper respiratory tract — the nose and sinuses
  • Lower respiratory tract—the airways and lungs

The upper respiratory tract filters out particles such as dust and germs in the air we breathe. It also warms and moistens the air.

The lower respiratory tract starts at the windpipe (trachea) just below the vocal cords and keeps branching until it gets to the air sacs. The air sacs are where oxygen – O2 enters to blood (“in with the good air”) and the carbon dioxide – CO2 comes out (“out with the bad air”). The tubes that go from the windpipe to the air sacs are called the “airways.”

The airways have cells with special housecleaning tools called cilia that are like small hairs. They move together to push the dust, germs and mucus out of the lungs where it can be coughed out. The cilia are normally bathed in a thin layer of fluid that is kept at just the right volume and has a mixture of chemicals (like sodium and chloride) and special chemicals that help fight infections.

Cystic fibrosis (CF) is caused by abnormalities in a protein called CFTR (cystic fibrosis transmembrane conductance regulator). This protein normally ends up on the surface of cells in the lungs — and in the pancreas and other organs — where it does some of the basic “housecleaning” at the level of the cells.

In the lungs, when CFTR works correctly it helps move chloride, water and other small molecules out of the cells and onto the surface of the airways.

But with CF, this protein doesn’t get to the cell surface, or it’s there but doesn’t function properly. The right amounts of chloride, water and other molecules do not move into the airways and the lungs cannot do their normal microscopic housecleaning.

Without the body’s typical cleaning process, the airways get into a cycle of inflammation (swelling) and infection, causing mucus and bacteria to build up in the lungs of people with CF.

Monitoring and minimizing this buildup of mucus and bacteria are two key jobs of your CF care team. See Work with Your CF Team for more information.

Click here to see more detailed information about DNA.

Beyond the Basics  

The key protein in cystic fibrosis is CFTR. The genetic “blueprint” for CFTR, and for all proteins in the body, lies in the DNA code that determines our body’s basic makeup. 

In people with CF, the instructions for the CF gene have been altered, creating a defective gene, which in turn produces a faulty CFTR protein. 

More than 1,500 mutations in the CF gene have been identified. The relationship between an individual’s CF mutation (“genotype”) and the way that the disease actually affects that person’s body (“phenotype”) is complex.

In some mutations, no CFTR protein is made at all. In others, CFTR is made but then gets “stuck” and doesn’t move from the center of the cell to the surface. Some mutations make the protein and it gets to the cell surface but it works too weakly to do its job.

Different therapies may be useful for different CF mutations. If you have not been “genotyped” or tested to find out which CF mutation or mutations you have, this is something to talk about with your CF caregiver.

Additional Resources

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Updated 07/16/12