The Sweat Gland
Sweat is produced in glands under the skin, transported to the skin surface through ducts, where some of the salt and water are reabsorbed. In normal skin functioning, as sweat moves along the duct most of the sodium and chloride -- the components of salt -- are reabsorbed. This is driven by a large force drawing sodium into cells lining the sweat duct. The chloride flows through the CFTR channel, while sodium flows into the cell through epithelial sodium (Na) channels (ENaC) in the apical membrane.

The salt reabsorption process is markedly abnormal in people with CF. Chloride transport is virtually eliminated because CFTR, which is the main way for chloride to enter the apical, or top, surface of cells is defective. Chloride must travel through the CFTR, located on the surface of the duct cells, at the same rate as sodium to maintain a balance of electrical charges. This results in very little sodium and chloride reabsorption, leading to a high salt content in CF sweat -- so high that the sweat chloride concentration is the most reliable single test for CF.

The Lung
The lung’s airways are covered with a thin, moist film called airway surface liquid, or ASL, a salt-containing liquid and a mucus gel layer. The ASL traps bacteria and foreign particles, while cilia on the surface of airway cells constantly move the particles out of the lungs and toward the mouth. This process, called mucociliary clearance, or MCC, is an important defense mechanism that protects the lungs from infection. ASL also contains antiproteases, antioxidants, antibodies and other substances that work together to neutralize or destroy invading organisms without damaging the lungs. In CF airways, decreased chloride transport is coupled with excess sodium transport out of the surface liquid. Since water follows the flow of sodium, the ASL loses volume and the mucus gel layer becomes dehydrated.

Select the "Lung - Airway Cell" or "Sweat Gland Cell" above to compare the functionality of a normal cell to a cell with CF.

The Pancreas
Pancreatic gland cells secrete digestive enzymes that join a bicarbonate (HCO3)-rich fluid secreted by cells lining the pancreatic ducts. This combination forms an alkaline, or non-acidic, mixture which maximizes enzyme function. Enzymes are proteins that speed up chemical reactions; without them, our bodies would grind to a halt. In CF patients, pancreatic gland cell secretion may be normal, while bicarbonate fluid secretion decreases. The two transport pathways at the apical cell membrane involved in bicarbonate secretion, and the way the CFTR interacts with these exchangers, are under investigation.