Explain how cystic fibrosis affects digestion, gas exchange and reproduction.

Background information I would give to the student: This question is a perfect example which shows that if you really understand the topic, it becomes easier to remember the facts for the questions relating to it. In order to answer this question, it is important to know what Cystic Fibrosis is. It is a disease where there is a genetic mutation in the CFTR gene which codes for the CFTR protein. The CFTR protein allows movement of chlorine outside the cell to the epithelium layer, which inhibits sodium moving into the cell from the epithelium surface. It is also important to know that water movement is linked to sodium movement- water follows sodium. So when the CFTR protein is faulty, there is no chlorine movement outside the cell. As a result, there is no inhibition of sodium movement into the cell and water will follow due to osmosis. This makes the mucus in the epithelium surface thick and sticky as water has been removed from it. Now using knowledge of this, we can explain how this would affect digestion, reproduction and gas-exchange.
In terms of gas-exchange, mucus lines the airways of the lungs. Specialized hair cells in the lining of the airways, called cilia, waft the mucus away. You can think of the cilia acting like an escalator to the mucus, it keeps it moving up and out of the airways making sure it does not build-up. So now that the mucus is thicker, the cilia cannot waft the mucus away and it builds up. Pathogens, such as bacteria trapped in the mucus increase the possibility of infection. Mucus also blocks the bronchioles which reduce the surface area of the alveoli in contact with gas, and thus decreases gas-exchange.
Digestion is aided by digestive enzymes which are released by the pancreas via the pancreatic duct into the duodenum (small intestine). The pancreatic duct is lined by mucus. Thicker mucus means that digestive enzymes are not secreted properly, meaning food is not digested properly. This can lead tiredness and weight loss. In addition, the enzymes trapped in the pancreatic duct can damage the insulin-producing cells in the pancreas, leading to diabetes.
In terms of reproduction, mucus lines the cervix. During sexual intercourse, sperm is released into the cervix and must travel through the cervix to reach the egg. Thick mucus prevents entry of the sperm through the cervix and thus reduces the chance of fertilization. The sperm duct in males carries sperm from the testes to the urethra and is lined with mucus. Thick mucus can prevent sperm leaving the testes.