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Cystic fibrosis pathophysiology
Video transcript
- [Voiceover] So the gene
that's not working well in cystic fibrosis is
called the "CFTCR" gene. So, my gosh, it's a long
acronym and it stands for, let's write this quickly,
Cystic Fibrosis, so they obviously named this after
they named the disease. Cystic Fibrosis Transmembrane, which means it goes from one side of
the membrane to the other. Conductance is letting things through, across a membrane, from
one side to the other. And then Regulator. So it controls the movement of something, going cross a membrane. The two ions that are affected
are chloride and sodium. But keep in mind that CFTCR
is a chloride channel. So chloride is physically being blocked by this channel not working. And sodium is affected
because it has a relationship with chloride, but sodium
has its own channel, which is not affected in cystic fibrosis. This CFTCR gene is all over
the body, and depending on where it is, the
situation's a little different. But the common rule's the same, and to illustrate this, let's talk about the sweat gland. This is a place where
this gene has a big role. And from this example,
it's kinda the same thing, going across the body for
cystic fibrosis symptoms. So if this is our sweat
gland, it starts here. So what is secreted into
here that's a channel, and then here is the surface to our skin. I'm gonna label this side "Skin". So when sweat is first
secreted by this gland, it's a lot of sodium and chloride in it. For sodium, let's use blue. Notice that it has a plus charge. Sodium all over here. At the same time, there's
also a lot of chloride in it. Chloride has a negative sign. As you can see in nature, positive and negative attract, right? So, sodium and chloride like
to balance each other out. And they're friends. In other words, the body likes the amount of sodium chloride to be about balanced. So going along this sweat gland, going towards the skin,
there's gonna be channels to reabsorb this chloride
and sodium into the body. We don't want to secrete it all out. So for sodium, we have its own channels, and we use blue here. And then just dot it along the way. Of course, next to them
there's the chloride channels. Now these channels are the ones that are affected by our CFTCR thing. I wanna label this, so CFTCR. In cystic fibrosis, these
channels are not working. But let's look at this as a normal one. So, let's see, this is normal sweat gland. And normally, as the
chloride flows down here, everything goes this way as it
floats down here, it'll leave through these channels
and go back into the body. So this face here, is the body. That's the skin, that's the outside. So these, as they go along,
they go back into the body. And sodium does the same thing. Remember that we want to keep our amount of sodium and chloride pretty balanced. So as the chloride leaves, so does the sodium, through their channels. And they kinda keep an eye on each other to make sure that their
numbers are about balanced. So when we get to the end
here, let's say that there's, let's just say there're
two sodium molecules left, and their buddies, two chloride ions. Now sodium chloride, this is table salt. So this is why our sweat tastes
slightly salty on our skin. And this is normal, because not all of the sodium and chloride will be reabsorbed. Just as an aside, have you noticed that when you sweat a lot, it
gets to be a little saltier, or the sweat has a stronger smell? That's because this is going
through this channel faster, when you're sweating a
lot, and there's less time for these reabsorptions,
so there's more salt left. But that's still normal. Here, let's look at a channel with in a person with cystic fibrosis. So same channel, structurally everything's gonna be the same. And here I'm gonna label this one "CF". Now initially the sweat, the content of it being secreted into here is the same. So I'm gonna use the little dots instead of writing it out this time. You already know blue is
sodium, and orange is chloride. So same channels for the sodium, and they're working just the same. So no problem with sodium channels. However, this time the
CFTCR gene is not working, so the chloride channels
are all messed up. So they look like this, it's not open. So as the chloride floats
down this way, it can't leave. Do you see, it just has to stay in here, and it keeps going towards the skin. And sodium, at this point, it sees that the chloride
is still in here. The negative and positive
want to stay together, so even though the sodium channel is open, the sodium doesn't go either, because its buddy
chloride is still in here. And the body won't just take the positive sodium ions, and leave
the negative in here. It has to be balanced. So, same thing, the sodium gets trapped in here, too,
pulled by the chloride. So in this person, when
we get to the skin, it's almost the same content
of sodium chloride as before. As you can see this is a lot
more than just two of each. Now, I chose two as just
an arbitrary number, but just to show you that
this one is gonna have a lot more, and this is a
lot saltier on the skin. So one of the symptoms of
having CF is having salty skin, or even a baby we do a
chloride test to see how much chloride is on the skin,
and that can point to CF. But the pathophysiology of this channel is similar throughout the body. I just chose one organ here to show you. Now really quickly, in the lungs, the problem is secreting chloride across the epithelium
to moisten the lungs. And since the chloride can't get secreted, the sodium also doesn't get secreted. And water follows sodium. So that's why the
secretions are really thick, because they're lacking in water. And that's how you get
the thick secretions in the lungs and in the pancreas. But here in the skin you get salty sweat.