The Lungs.

Cystic fibrosis make a person sick by disrupting the normal function of epithelial cells - cells that make up the sweat glands in the skin and that also line passageways inside the lungs, liver, pancreas, and digestive and reproductive systems.

In CF, the inherited CF gene directs the body's epithelial cells to produce a defective form of a protein called CFTR.

When the CFTR protein is defective, epithelial cells can't regulate the way chloride (part of the salt called "sodium chloride") passes across cell membranes.

This disrupts the essential balance of salt and water that is needed to maintain a normal thin coating of fluid and mucus inside the lungs, pancreas, and passageways in other organs.

The mucus becomes thick, sticky, and hard to move.

Normally, mucus in the lungs traps germs, which are then cleared out of the lungs.

But in CF, the thick, sticky mucus and the germs it has trapped remain in the lungs, and the lungs become infected.

The frequent infections damage the lung and ultimatly a lung transplantation is the only way to keep a Cystic Fibrosis patient alive.