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How Cystic Fibrosis Affects Breathing and the Lungs - Topic Overview

Normal lung and respiratory function

The breathing tubes, or bronchi, leading to the air sacs (alveoli) are lined with cells that produce mucus. Normally, the cells produce a thin, runny mucus that coats the surface of the airways.

Foreign particles, such as dust and germs, constantly enter the airways and become trapped in the mucus. Tiny hairs called cilia on the surface of the breathing tubes sweep the mucus and foreign particles upward into the larger air passages and then up to the throat where they can be swallowed or coughed up.

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Effects of cystic fibrosis on lung and respiratory function

Cystic fibrosis causes the mucus that coats the breathing tubes to become so thick and sticky that the cilia are unable to sweep the germs and other particles up and out of the lungs. The trapped bacteria lead to frequent, serious infections and permanent lung damage.

In response to infections, the body's immune system sends white blood cells to the lungs to attempt to destroy the infection. White blood cells release chemicals that kill both bacteria and surrounding normal cells. After attacking the bacteria, the white blood cells die, adding to the thickness of the mucus and destruction of the airways.

In the upper respiratory tract, thick, sticky mucus may also clog the nasal passages and sinuses. Small growths, or polyps, on the inner lining of the nose may develop from repeated infection and inflammation.


Complications of cystic fibrosis usually involve some aspect of long-term impaired respiratory function. These complications may include:

  • Coughing up blood. Coughing up small amounts of blood is often a symptom of chest infection. Coughing up very large amounts of blood can be life-threatening. If you are coughing up blood, call your doctor.
  • Pneumothorax, a buildup of air between the lungs and chest wall that causes the lung to collapse. This affects adults with cystic fibrosis more often than children.
  • Enlargement of the right side of the heart. Over time, this can cause heart failure and death.
  • Increased pressure in the lungs (pulmonary hypertension). The arteries in the lungs narrow (constrict) in response to impaired oxygen flow between the lungs and blood cells. The heart must pump harder to move blood through the blood vessels, which increases pressure in the lungs.
  • Enlarged, damaged airways (bronchiectasis) which can lead to infection.

    WebMD Medical Reference from Healthwise

    Last Updated: September 09, 2014
    This information is not intended to replace the advice of a doctor. Healthwise disclaims any liability for the decisions you make based on this information.
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