Melissa Benoit

How does a problem in a salt channel lead to the lung problems in CF?

 In the lungs, the CFTR protein sits in the outer membrane of the cells and acts as a channel for chloride, moving it out of the cell.  CFTR also controls another channel called ENaC which is responsible for moving sodium into the cell.  When CFTR is not present or functioning properly, there is excessive sodium moving into the cell and not enough chloride leaving the cell. Movement of salt (sodium plus chloride) affects the movement of water so in the case of someone with CF, water moves from the airway into the cell.  This makes the mucous in the airways thicker (more dehydrated) than normal. 

 The surface of the airways are covered by a thin layer of mucous.  This mucous traps bacteria and other particles that are breathed into the lung.  The mucous is moved along the airways by little hairs on the surface of the cells called "cilia". The job of the cilia is to sweep the mucous out of the lung.  It is much harder for the thick mucous in CF to be moved out of the lung by the cilia.  In order to try and get rid of the mucous, you need to cough.  

 The nutrients and lack of oxygen in the mucous creates the perfect environment for certain bacteria to thrive in your lungs. Thus in CF, bacteria start to grow in the  mucous inside the airways. The immune system of the body is alerted and sends cells to try and kill the bacteria.  Over time these immune cells cause inflammation damaging the lungs and causing the cells to make more mucous. This creates a vicious cycle of mucous plugging of airways, infection, inflammation and more mucous plugging.