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Cystic fibrosis is an inherited, chronic and progressive condition characterized by dysfunction of the exocrine glands, primarily in the respiratory, gastrointestinal, and reproductive systems.
First, let’s quickly review some physiology. Exocrine glands are found throughout the body, and their main function is to secrete products like sweat from the skin; as well as saliva, gastric or pancreatic juices, and bile from the gastrointestinal tract; in addition to mucus to protect the respiratory, gastrointestinal, and reproductive systems, as well as seminal fluid from the prostate.
Now, zooming in, the exocrine glands consist of cells that secrete their products containing substances like water, ions, and enzymes into a ductal system. To do so, these cells have a special transporter protein called cystic fibrosis transmembrane conductance regulator protein, or CFTR for short. This protein pumps chloride ions out of the cell in order to help draw water out, forming those products and thinning them out, as needed for secretion.
Alright, so the main cause of cystic fibrosis is a mutation in the CFTR gene, which codes for the CFTR protein. This mutation is inherited with an autosomal recessive pattern, meaning that an individual needs to inherit one mutated gene from each parent to develop the condition. Thus, the main risk factor for cystic fibrosis is family history. In addition, another risk factor seems to be race and ethnicity, being more prevalent among individuals of white race.
Now, the pathology of cystic fibrosis develops because the mutated CFTR protein can’t insert into the cell membrane. As a result, exocrine cells can’t pump chloride ions out, so water doesn’t get drawn in, and the secretions are left overly thick. This can affect various organs in different ways.
In the respiratory tract, the thick mucus traps pathogens but can’t be swept up and out by cilia. As a consequence, these pathogens are able to remain in the lungs and keep replicating, which can lead to chronic respiratory infections, like pneumonia, and complications such as bronchiectasis, and even pneumothorax.
In the gastrointestinal tract, thick secretions can plug the pancreatic ducts, preventing the secretion of digestive enzymes into the small intestine. Over time, the backed-up digestive enzymes can degrade the cells lining the pancreatic ducts, which causes local inflammation and damage. This can ultimately lead to complications like pancreatitis, pancreatic insufficiency, and even diabetes.
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