Cystic Fibrosis and the Mucociliary System

Cystic Fibrosis and the Mucociliary System


You walk into a busy restaurant. Instinctively, you take a deep breath to smell
the wonderful aromas in the air. You also just inhaled thousands of bacteria
and viruses, many of which can cause disease like colds and pneumonia. So why don’t we constantly get sick? That’s because we’re protected by an excellent
defense system in our airways. Gooey mucus coats the surfaces of your airways,
trapping inhaled bacteria and viruses. Cilia, which are small hair-like protrusions
on cells, can sweep the mucus up and out of the airways. Together, the mucus and cilia form the mucociliary
system, which protects us against the germs we inhale. We can either cough or sneeze the dirty mucus
out, or subconsciously swallow it to kill the germs with acid in the stomach. If something is preventing the mucociliary
system from working, it makes sense that we would get sick more often. This is exactly what happens in people with
cystic fibrosis. Their mucus becomes so thick and dry that
cilia are unable to sweep it out of the airways. This leads to massive infections that eventually
are the cause of death for people with cystic fibrosis. As well, the mucus can build up and clog the
airways, making breathing difficult. What causes this thickening of the mucus? To answer that question, we need to zoom in
on one of these airway cells. On the membrane of this airway cell, we can
find the cystic fibrosis transmembrane conductance regulator, or CFTR. CFTR is an ion channel that allows chloride
ions to exit the cell and into the mucus. In cystic fibrosis, the gene coding for CFTR
has certain mutations which cause it to be in an incorrect shape or not even be in the
membrane at all. This means that chloride ions are no longer
able to exit the cell. A broken CFTR also leads to increased activity
of another ion channel called the epithelial sodium channel, or ENaC, by a mechanism that
is still being researched by scientists. ENaC allows sodium ions to enter the cell. The end result is a higher concentration of
ions inside than outside the cell. Concentration is a ratio of the amount of
ions to the volume of water they are dissolved in. You can increase concentration by increasing
the amount of ions or decreasing the amount of water. If two areas have different concentrations
of ions, and are separated by a barrier that only allows water through, osmosis will spontaneously
occur. Osmosis is the movement of water from an area
with low concentration to an area with high concentration, making both areas have equal
concentration. This is best observed in a U-shaped container
like this one, where it is clear that the side with more ions will end up with more
water. The analogy is that the side with less ions
is the mucus and the side with more ions is the cell, with the cell membrane separating
the two areas. Back to the cell. Osmosis will cause water in the mucus to cross
the cell membrane and into the cell. This dries out the mucus, making it thick
and very difficult for cilia to move around in, preventing the sweeping of mucus out of
the airways. As mentioned earlier, this results in infection
and airway blockage. CFTR and mucus are also found in the digestive
ducts right where the stomach and small intestine connect. These ducts allow bile from the gallbladder
and enzymes from the pancreas to enter the small intestine. These substances are important because they
help digest food. Defective CFTR can once again lead to mucus buildup
in the ducts, clogging them and preventing release of those digestive substances. Therefore, another symptom of cystic fibrosis
is malnutrition as food cannot be broken down properly. Sweat glands also have CFTR, except they allow
chloride ions to enter cells, opposite of what happens in the airways and gut. Normally, this reverse direction prevents
too much electrolyte loss from sweating. However, with defective CFTR, chloride ions accumulate
in the sweat and combine with sodium ions to produce salt. Abnormally salty sweat is therefore another
symptom that can be used to diagnose cystic fibrosis. Therefore, the main symptoms of people suffering
from cystic fibrosis are clogged and infected airways, malnutrition from clogged digestive
ducts, and very salty sweat. All of these are caused by a genetic mutation
in the CFTR gene, leading to defective CFTR. Because it is a genetic disease, rates of
cystic fibrosis differ with ethnicity. This disease affects Caucasians the most,
with 1/3000 Caucasians affected, followed by African-Americans and Asians, with over 70,000 people affected worldwide. Advancements in medicine have increased the
average lifespan of people with cystic fibrosis from 14 years in the 1980s to 40 years now
and growing. Some of these medications include digestive
enzyme and vitamin supplements that can treat the effects of malnutrition. Antibiotics can treat infections. Medication that breaks down mucus or expand
the airways can treat blockage of airways. However, these medications only treat the
symptoms and not the cause of the disease, which is defective CFTR. New medications are now being researched that
can make CFTR functional again, called CFTR potentiators. These have only worked for approximately
5% of people with cystic fibrosis that have a certain mutation, but the other 95% is still
desperately in need of a cure. To learn more about cystic fibrosis or donate
to its research to help find a cure for this debilitating disease, check out Cystic Fibrosis
Canada, the Cystic Fibrosis Foundation, or other organizations
involved in cystic fibrosis in your area. Thanks for watching, and see you next time
for another explanation of a disease on Medicurio.

42 Replies to “Cystic Fibrosis and the Mucociliary System

  1. Thank you so much for this, there's a huge lack of information explaining how certain diseases result in their set of symptoms. I really look forward to more videos like this 🙂 subbed.

  2. Thanks for this. My Grandma had Cystic Fibrosis and was told she wouldn't live to be 20 but lived to 60 and up to now the only thing I new about it was it had something to do with mucus in the lungs. I've been told I am a carrier (male) and I was wondering if you could explain what this means for any children I have in the future..

  3. Reddit brought me here!
    This is really cool man, thanks for this. Please keep it up! I found it super interesting.
    Is there any chance you'll be doing one on Eczema?

  4. Great video, very informative. Maybe a prognosis toward the end?–I know the mortality rate is unfortunately high, but don't know details.
    You said on Reddit this is a new series — good luck! This was informative and interesting. The pacing could be accelerated.

  5. I know this sort of thing isn't especially engaging for a person unaffected by the condition, not taking a class involving these mechanisms, or someone not in a related field…but as someone of none of those, I really enjoyed the video. This is the sort of channel I can see growing! Like when you see massive edutainment channels with amazing graphics…they started out with complicated concepts made entertaining by a common digestible thread…entertainment. This was entertaining.

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