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.